# NTSB CEN20LA292: Beech A23-24, N3412C, Burns Flat, OK, July 19, 2020 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: July 18, 2020, 22:45 local (Jul 19, 2020, 03:45 UTC) - Place: Burns Flat, OK - Coordinates: 35.381668, -99.20111 - Nearby events: https://openairdocs.org/map.md?lat=35.3817&lon=-99.2011&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: 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: Central Region - Parties: Federal Aviation Administration, Oklahoma City - NTSB case key (mKey): 101629 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN20LA292 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/101629/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=101629 - Page: https://openairdocs.org/ntsb/CEN20LA292 ## Probable cause The mechanic’s improper maintenance when he reinstalled the fuel servo during the last annual inspection, which resulted in a loss of engine power during cruise flight when the throttle control rod-end disconnected from the fuel servo throttle linkage. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine controls: power lever](https://openairdocs.org/ntsb-findings/01057603): Aircraft › Aircraft power plant · Inoperative (probable cause); cases with it: [Beech A23-24, 1 case](https://openairdocs.org/ntsb-findings/01057603/cases.md?model=1151226), [All aircraft, 95 cases](https://openairdocs.org/ntsb-findings/01057603/cases.md) - [Engine controls: power lever](https://openairdocs.org/ntsb-findings/01057603): Aircraft › Aircraft power plant · Incorrect service/maintenance (probable cause); cases with it: [Beech A23-24, 1 case](https://openairdocs.org/ntsb-findings/01057603/cases.md?model=1151226), [All aircraft, 95 cases](https://openairdocs.org/ntsb-findings/01057603/cases.md) - [Misc hardware: fasteners](https://openairdocs.org/ntsb-findings/01071430): Aircraft › Fluids/misc hardware · Incorrect service/maintenance (probable cause); cases with it: [Beech A23-24, 1 case](https://openairdocs.org/ntsb-findings/01071430/cases.md?model=1151226), [All aircraft, 58 cases](https://openairdocs.org/ntsb-findings/01071430/cases.md) - [Maintenance: installation](https://openairdocs.org/ntsb-findings/02062035): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Beech A23-24, 1 case](https://openairdocs.org/ntsb-findings/02062035/cases.md?model=1151226), [All aircraft, 371 cases](https://openairdocs.org/ntsb-findings/02062035/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Prior to flight: Aircraft inspection event](https://openairdocs.org/ntsb-events/050); cases with it: [Beech A23-24, 1 case](https://openairdocs.org/ntsb-events/050/sequence.md?model=1151226), [All aircraft, 229 cases](https://openairdocs.org/ntsb-events/050/sequence.md) - [Enroute-cruise: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Beech A23-24, 1 case](https://openairdocs.org/ntsb-events/342/sequence.md?model=1151226), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Landing: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Beech A23-24, 5 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=1151226), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) ## Analysis The pilot and his 3 passengers were on a personal night flight when the airplane had a gradual loss of engine power. The pilot was unable to restore engine power and a forced landing was completed to a grass field. The airplane’s main landing gear collapsed when the pilot intentionally swerved the airplane to avoid a tree after landing, which resulted in substantial damage to the horizontal stabilizer and both wings. A postaccident examination revealed that the throttle control rod-end was not connected to the fuel servo throttle linkage. Additionally, the required retaining bolt, washer, and self-locking nut were not located during the investigation. The airplane had accumulated 8.72 flight hours since the last annual inspection, during which the fuel servo had been removed from the engine and overhauled. It is likely that the mechanic who reinstalled the fuel servo did not adequately torque the self-locking nut that secured the retaining bolt, which allowed the self-locking nut to back-off the retaining bolt. The airplane had a partial loss of engine power when the throttle control rod-end disconnected from the unsecured retaining bolt. The pilot did not have the ability to control engine power after the throttle control rod-end disconnected from the fuel servo throttle linkage. ## Factual narrative On July 18, 2020, about 2245 central daylight time, a Beech A23-24 airplane, N3412V, was substantially damaged when it was involved in an accident near Burns Flat, Oklahoma. The pilot and his 3 passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that while established in cruise flight the airplane had a gradual loss of engine power. He was unable to restore engine power by switching fuel tanks, turning on the fuel boost pump, and advancing the throttle, mixture, and propeller controls full forward. The pilot made a forced landing in a grass field. After touchdown the airplane traversed over 3 large terraces, and the main landing gear collapsed when the pilot tried to swerve the airplane to avoid a tree. The horizontal stabilizer and both wings were substantially damaged during the forced landing. The airplane was examined at the accident site by a Federal Aviation Administration airworthiness inspector. Both wing fuel tanks contained about 25 gallons of 100 low-lead aviation fuel. The throttle control was very loose when moved by hand in the cockpit. A visual examination revealed that the throttle control rod-end was not connected to the fuel servo throttle linkage. (Figure 1) The required retaining bolt, washer, and self-locking nut were not located during the investigation. Figure 1. Throttle control rod-end found disconnected from the fuel servo throttle linkage. The airplane had accumulated 8.72 flight hours since the last annual inspection that was completed on October 22, 2019. The inspection authorized (IA) mechanic who had completed the annual inspection stated that the fuel servo had been removed from the engine and overhauled in conjunction with the annual inspection. The IA mechanic stated that he personally reinstalled the overhauled fuel servo on the engine, while another individual moved the throttle and mixture controls in the cockpit. The IA mechanic stated that it is his standard practice to connect both the throttle and mixture controls to the fuel servo at the same time. The IA mechanic stated that he likely reused the bolt and washer to connect the throttle control rod-end to the fuel servo throttle linkage, and that it is also possible that he reused the self-locking nut. However, he would not have reused the self-locking nut if it had fully engaged the bolt threads by hand. The IA mechanic stated that he used two wrenches to secure the self-locking nut and that he did not use a torque wrench. A review of the Beech A23-24 Maintenance Manual revealed no specific assembly instructions on how to physically connect the throttle control rod-end to the fuel servo throttle linkage. The Beech A23-24 Illustrated Parts Catalog specified that the throttle control rod-end be attached to the fuel servo throttle linkage with a 169-910021 bolt, AN960-10 washer, and MS20365-1032 self-locking nut. ## Aircraft - Registration: [N3412C](https://openairdocs.org/aircraft/N3412C), registered now, S/N MA-357, built 1969 (OpenAirDocs) - Reported make and model: Beech A23-24 - Registry model: [Beech A23-24](https://openairdocs.org/model/beech-a23-24) (registry code 1151226) (OpenAirDocs) - Registry engine: [Lycoming I0360 series](https://openairdocs.org/engine/lycoming-i0360-series) (registry code 41515, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: MA-357 - Year built: 1969 - Airframe hours: 1717.76 - Engines: Lycoming IO-360-A1B 200 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: Annual, October 22, 2019, 8.72 hours before - Departed: ELK, Elk City, OK - Equipment: Stall warning system, Handheld GPS ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 27; injuries: none; private; airplane ratings: single-engine land; medical: class 3, with waivers/limitations; last flight review July 3, 2020; seat: left; restraint: lap only; flight hours: 309.6 total, 8.4 in this make and model, 267.6 as pilot in command, 8.4 in the last 90 days, 8.4 in the last 30 days, 1.5 in the last 24 hours ## Weather - Conditions: Visual (VMC), Night/dark - Wind: 160° at 17 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 82 °F, dew point 66 °F - Altimeter: 29.98 inHg - Observed at: CSM, 2.5 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 20200718019159A](https://openairdocs.org/incident/20200718019159A), Jul 18, 2020: Beech A23-24, Burns Flat, OK, Substantial damage. The aircraft departed kelk, elk city Oklahoma for a part 91 personnel night VFR local flight. The pilot was properly rated and the aircraft was in annual. The… ## Docket (8 files) The files NTSB released with the investigation on February 24, 2022, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=101629. 4.9 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 10 pages, 1.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11668632&FileExtension=pdf&FileName=01%20-%20Pilot%20Report_Redacted-Rel.pdf - FAA inspector statement (item 2, PDF, 1 page, 64 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11668295&FileExtension=pdf&FileName=02%20-%20FAA%20Inspector%20Statement-Rel.pdf - Memorandum of conversation (item 3, PDF, 1 page, 74 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11668192&FileExtension=pdf&FileName=03%20-%20Memorandum%20of%20Conversation%20(Michael%20R%20Hall)-Rel.pdf - Airplane maintenance logbooks (excerpts) (item 4, PDF, 3 pages, 627 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11668642&FileExtension=pdf&FileName=04%20-%20Airplane%20Maintenance%20Logbooks%20(Excerpts)_Redacted-Rel.pdf - Airplane maintenance shop manual (excerpts) (item 5, PDF, 2 pages, 298 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11668202&FileExtension=pdf&FileName=05%20-%20Airplane%20Maintenance%20Shop%20Manual%20(Excerpts)-Rel.pdf - Airplane illustrated parts catalog (excerpts) (item 6, PDF, 3 pages, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11668652&FileExtension=pdf&FileName=06%20-%20Airplane%20Illustrated%20Parts%20Catalog%20(Excerpts)-Rel.pdf - Weather (item 7, PDF, 1 page, 102 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11668082&FileExtension=pdf&FileName=07%20-%20Weather-Rel.pdf - Photos (item 8, PDF, 3 pages, 3 photos, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11667775&FileExtension=pdf&FileName=08%20-%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.