# NTSB CEN23LA107: Mooney M20, N304MA, Lakeway, TX, February 12, 2023

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Class 3 · Limited · Final report
- Date: February 12, 2023, 09:58 local (15:58 UTC)
- Place: Lakeway, TX · Golf course.
- Coordinates: 30.363162, -97.995269 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=30.3632&lon=-97.9953&mi=10
- Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping)
- Defining event: [Approach-VFR pattern downwind: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed
- Report: Approved by Office Director
- Investigation class: Class 3
- NTSB office: Central Region
- Parties: Mooney International Corporation, Hartzell Propeller / Hartzell Engine Technologies, FAA San Antonio FSDO
- NTSB case key (mKey): 106726
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN23LA107
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/106726/pdf
- NTSB docket: https://data.ntsb.gov/Docket?ProjectID=106726
- Page: https://openairdocs.org/ntsb/CEN23LA107

## Probable cause

A total loss of engine power due to detonation and preignition in the No. 6 cylinder.

## Findings

NTSB's coded findings; those marked are part of the probable cause.

- [Engine (reciprocating)](https://openairdocs.org/ntsb-findings/01058500): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Mooney M20K, 3 cases](https://openairdocs.org/ntsb-findings/01058500/cases.md?model=5870220), [All aircraft, 497 cases](https://openairdocs.org/ntsb-findings/01058500/cases.md)
- [Engine (reciprocating)](https://openairdocs.org/ntsb-findings/01058500): Aircraft › Aircraft power plant · Incorrect use/operation (probable cause); cases with it: [Mooney M20K, 3 cases](https://openairdocs.org/ntsb-findings/01058500/cases.md?model=5870220), [All aircraft, 497 cases](https://openairdocs.org/ntsb-findings/01058500/cases.md)

## Sequence of events

The events NTSB coded, in order, by phase of flight. The defining event best describes what happened.

- [Enroute: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342); cases with it: [Mooney M20K, 4 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=5870220), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md)
- [Enroute: Attempted remediation/recovery](https://openairdocs.org/ntsb-events/060); cases with it: [Mooney M20K, 2 cases](https://openairdocs.org/ntsb-events/060/sequence.md?model=5870220), [All aircraft, 1,422 cases](https://openairdocs.org/ntsb-events/060/sequence.md)
- [Approach-VFR pattern downwind: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Mooney M20K, 15 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=5870220), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md)
- [Approach-VFR pattern downwind: Attempted remediation/recovery](https://openairdocs.org/ntsb-events/060); cases with it: [Mooney M20K, 2 cases](https://openairdocs.org/ntsb-events/060/sequence.md?model=5870220), [All aircraft, 1,422 cases](https://openairdocs.org/ntsb-events/060/sequence.md)
- [Approach-VFR pattern final: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Mooney M20K, 14 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=5870220), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md)
- [Post-impact: Evacuation](https://openairdocs.org/ntsb-events/460); cases with it: [Mooney M20K, 1 case](https://openairdocs.org/ntsb-events/460/sequence.md?model=5870220), [All aircraft, 103 cases](https://openairdocs.org/ntsb-events/460/sequence.md)

## Analysis

Before purchasing the airplane, the pilot had an inspection performed. One of the findings on the inspection stated that, “spark plugs are worn past limits.” There were no indications that the magneto timing was checked during the inspection. The pilot reported that the airplane had been run with a lean mixture in the past. After the pilot purchased the airplane, he flew the airplane on a cross-country flight to relocate it to his home base. While in flight, the engine had a low manifold pressure reading and then the engine sustained a total loss of power. The pilot attempted to fly to the nearest airport, but instead performed a forced landing to a golf course. During the forced landing sequence, the airplane impacted trees and a wood fence, and came to rest near a diesel generator. The airplane sustained substantial damage to the fuselage and to both wings. Examination of the airframe revealed no mechanical anomalies. Examination of the engine revealed a hole in the corner of the No. 6 piston; however, the No. 6 cylinder was intact. The No. 6 piston had eroded crown material and a darkened periphery. The engine case was found intact. The top spark plugs from the Nos. 3, 5, and 6 cylinders and the bottom spark plugs from the Nos. 3 and 5 cylinders were found in a “worn out - normal condition.” The right magneto timing was found at 22°, when it is supposed to be at 20°. The left magneto timing was found at 15°, when it is supposed to be at 20°. The oil breather tube was found intact, and the slot was not blocked. Engine oil was found splattered in and around the oil breather tube area, including traveling rearward on the area underneath the oil breather tube. No anomalies were noted with the turbocharger system or the propeller. It is likely a total loss of engine power occurred when the No. 6 piston developed a hole from burn through, consistent with detonation and preignition signatures consisting of combustion deposits and excessive temperature exposure. The hole in the piston likely allowed exhaust gases, caused by the detonation and preignition, to force engine oil out of the oil breather tube. The combination of the engine being previously run with a lean mixture, worn spark plugs, and incorrect magneto timing, likely lead to the preignition and detonation and a subsequent total loss of engine power.

## Factual narrative

On February 12, 2023, about 0958 central standard time, a Mooney Aircraft Corporation M20K Encore airplane, N304MA, sustained substantial damage when it was involved in an accident near Lakeway, Texas. The pilot sustained no injury. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal cross-country flight. The pilot reported that he had recently purchased the airplane and he was relocating the airplane to his home base at the Outlaw Field Airport (CKV), Clarksville, Tennessee. During the preflight inspection, the pilot did not observe any anomalies. He reported that the airplane had 57 gallons of fuel onboard at takeoff and the engine oil was at a sufficient level for flight operations. A review of ADS-B data showed that the airplane departed from the Kestrel Airpark (1T7), Spring Branch, Texas, and traveled to the northeast. The pilot reported that while in flight, the engine had a low manifold pressure reading and then the engine sustained a total loss of power. The ADS-B data showed that the airplane performed a 180° turn as it approached the Colorado River just to the north of Bee Cave, Texas. The pilot then maneuvered the airplane north toward the Lakeway Airpark (3R9), Lakeway, Texas. Unable to make the airport, the pilot performed a forced landing to a golf course just to the north of 3R9. During the forced landing, the airplane impacted trees and a wood fence, and came to rest upright near a diesel generator. The pilot was able to egress from the airplane without further incident. The airplane sustained substantial damage to the fuselage and to both wings. A Federal Aviation Administration (FAA) inspector responded to the accident site. A large amount of engine oil was observed trailing rearward on the underside of the fuselage. The engine oil level was checked at the accident site and oil was not observed on the dipstick. Examination of the airframe revealed flight control continuity. Both wing fuel tanks were found breached and no anomalies were noted with the airframe. Examination of the engine revealed a hole in the corner of the No. 6 piston; however, the No. 6 cylinder was intact. The No. 6 piston had eroded crown material and a darkened periphery. The engine case was found intact. The top spark plugs from the Nos. 3, 5, and 6 cylinders and the bottom spark plugs from the Nos. 3 and 5 cylinders were found in a “worn out - normal condition.” The right magneto timing was found at 22°; according to the engine manufacturer, it is supposed to be at 20°. The left magneto timing was found at 15°, rather than 20°. The oil breather tube was found intact and the slot was not blocked. Engine oil was found splattered in and around the oil breather tube area, including traveling rearward on the area underneath the oil breather tube. No anomalies were noted with the turbocharger system or the propeller. Before purchasing the airplane, the pilot had an inspection performed by a mechanic. One of the findings on theundated inspection list stated that, “spark plugs are worn past limits.” Additionally, all cylinders were borescoped and the cylinders were listed as, “all appear normal.” The pilot reported that there were no indications that the magneto timing was checked during the prebuy inspection. The pilot further reported that the airplane had been run with a lean mixture in the past. A review of the engine maintenance records showed that the most recent time the spark plugs were cleaned and gapped, and the magneto timing was checked was during a 100-hour inspection on October 8, 2022, at 2,732.4 hours. A review of data obtained from a J.P. Instruments EDM-700 unit onboard the airplane at the time of the accident showed an excessively high No. 6 cylinder head temperature reading about 17 minutes before the unit stopped recording data. The FAA has published the Pilot’s Handbook of Aeronautical Knowledge FAA-H-8083-25C. This document discusses detonation and states in part: Detonation is an uncontrolled, explosive ignition of the fuel-air mixture within the cylinder’s combustion chamber. It causes excessive temperatures and pressures which, if not corrected, can quickly lead to failure of the piston, cylinder, or valves. In less severe cases, detonation causes engine overheating, roughness, or loss of power. Detonation is characterized by high cylinder head temperatures and is most likely to occur when operating at high power settings. A common operational cause of detonation is listed as: Operation of the engine at high power settings with an excessively lean mixture. This document discusses preignition and states in part: Preignition occurs when the fuel-air mixture ignites prior to the engine’s normal ignition event. Premature burning is usually caused by a residual hot spot in the combustion chamber, often created by a small carbon deposit on a spark plug, a cracked spark plug insulator, or other damage in the cylinder that causes a part to heat sufficiently to ignite the fuel-air charge. Preignition causes the engine to lose power and produces high operating temperature. As with detonation, preignition may also cause severe engine damage because the expanding gases exert excessive pressure on the piston while still on its compression stroke. The document further discusses both detonation and preignition and states in part: Detonation and preignition often occur simultaneously and one may cause the other. Since either condition causes high engine temperature accompanied by a decrease in engine performance, it is often difficult to distinguish between the two. Using the recommended grade of fuel and operating the engine within its proper temperature, pressure, and rpm ranges reduce the chance of detonation or preignition. Continental Motors has published Mandatory Service Bullet MSB94-8D Magneto to Engine Timing on February 17, 2010. This document discusses the importance of maintaining correct magneto timing and states in part: Incorrect timing, inaddition to producing a rough running engine, can lead to detonation, preignition and internal engine damage or failure. Failure to properly maintain the magneto, harness and spark plugs will lead to internal engine damage and failure.

## Aircraft

- Registration: [N304MA](https://openairdocs.org/aircraft/N304MA), registered now, S/N 25-2004, built 1997 (OpenAirDocs)
- Reported make and model: MOONEY AIRCRAFT CORP. M20 (K)
- Registry model: [Mooney M20K](https://openairdocs.org/model/mooney-m20k) (registry code 5870220) (OpenAirDocs)
- Registry engine: [Continental TSIO-360 series](https://openairdocs.org/engine/continental-tsio-360-series) (registry code 17019, reciprocating) (OpenAirDocs)
- Category: Airplane
- Serial number: 25-2004
- Year built: 1997
- Airframe hours: 2763.7
- Engines: Continental Motors TSIO-360-MB 210 horsepower reciprocating
- Damage: Substantial damage
- Flight: Personal, Part 91
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, October 8, 2022, 31.3 hours before
- Departed: 1T7, Spring Branch, TX
- Destination: CKV, Clarksville, TN
- Flight plan: VFR
- Equipment: Electronic flight bag or handheld device, Electronic primary flight display, Stall warning system, ADS-B, Data recorder, Auto-pilot

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 52; injuries: none; flight instructor, commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane, helicopter; medical: class 2, without waivers/limitations; last flight review April 14, 2022; seat: left; restraint: 3-point; flight hours: 5,377.8 total, 7 in this make and model, 3,337.5 as pilot in command, 27.1 in the last 90 days, 12.7 in the last 30 days, 6.5 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 250° at 4 knots
- Visibility: 10 statute miles
- Lowest ceiling: none
- Temperature: 46 °F, dew point 32 °F
- Altimeter: 30.21 inHg
- Observed at: KRYW, 8 nm away
- METAR: KRYW 121555Z AUTO 25004KT 10SM CLR 08/00 A3021 RMK AO2 T00821003

## 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 20230212001079A](https://openairdocs.org/incident/20230212001079A), Feb 12, 2023: Mooney Aircraft Corp. M20K, Lakeway, TX, Substantial damage. On February 12, 2023, at approximately 0930 central daylight time, [privacy data omitted], a Mooney M20K, departed kestrel air park, Texas (1T7) for outlaw…

## Docket (22 files)

The files NTSB released with the investigation on September 11, 2024, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=106726. 146 MB in all.

- Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 11 pages, 6.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17057139&FileExtension=pdf&FileName=NTSB%20Form%206120_1_Redacted-Rel.pdf
- Various statements (item 2, PDF, 5 pages, 462 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17063714&FileExtension=pdf&FileName=Various%20Statements_Redacted-Rel.pdf
- Pilot - various emails (item 3, PDF, 11 pages, 939 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17141056&FileExtension=pdf&FileName=Pilot%20-%20Various%20Emails_Redacted-Rel.pdf
- Accident photographs (item 4, PDF, 21 pages, 4.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17145351&FileExtension=pdf&FileName=Accident%20Photographs-Rel.pdf
- Federal aviation administration - N304MA accident site maps (item 5, PDF, 2 pages, 383 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17060146&FileExtension=pdf&FileName=Federal%20Aviation%20Administration%20-%20N304MA%20Accident%20Site%20Maps-Rel.pdf
- N304MA - accident flight ADS-B data (google earth .kmz file) (item 6, KMZ, 102 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17054434&FileExtension=kmz&FileName=20230212_A32F42_507593932_ADSB-Rel.kmz
- N304MA - accident flight ADS-B data (microsoft excel .csv file) (item 7, CSV, 4.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17053972&FileExtension=csv&FileName=20230212_A32F42_507593932_ADSB-Rel.csv
- N304MA - prebuy inspection report (item 8, PDF, 1 page, 216 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17059816&FileExtension=pdf&FileName=N304MA%20-%20Prebuy%20Inspection_Redacted-Rel.pdf
- Airframe maintenance records - 2018 to accident (item 9, PDF, 18 pages, 37.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17141169&FileExtension=pdf&FileName=Airframe%20Maintenance%20Records%20-%202018%20to%20Accident_Redacted-Rel.pdf
- Engine maintenance records - 2018 to accident (item 10, PDF, 13 pages, 28.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17141507&FileExtension=pdf&FileName=Engine%20Maintenance%20Records%20-%202018%20to%20Accident_Redacted-Rel.pdf
- Propeller maintenance records - 2018 to accident (item 11, PDF, 4 pages, 6.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17141070&FileExtension=pdf&FileName=Propeller%20Maintenance%20Records%20-%202018%20to%20Accident_Redacted-Rel.pdf
- NTSB - N304MA airframe and engine examination report (item 12, PDF, 7 pages, 166 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17145934&FileExtension=pdf&FileName=CEN23LA107%20NTSB%20Examination%20Report-Rel.pdf
- Hartzell propeller - N304MA examination report (item 13, PDF, 9 pages, 3.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17059498&FileExtension=pdf&FileName=N304MA%20-%20Hartzell%20Propeller%20Examination%20Report_Redacted-Rel.pdf
- Materials laboratory factual report (item 14, PDF, 32 pages, 36 photos, 6.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16227428&FileExtension=pdf&FileName=23-076%20-%20Materials%20Lab%20Factual%20Report%20(CEN23LA107)-Rel.pdf
- NTSB - N304MA fuel flow transducer examination report (item 15, PDF, 3 pages, 291 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17060048&FileExtension=pdf&FileName=NTSB%20Fuel%20Flow%20Transducer%20Examination%20Report-Rel.pdf
- Engine data monitors - specialist's factual report (item 16, PDF, 12 pages, 11 photos, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16368357&FileExtension=pdf&FileName=ENGINE%20DATA%20MONITORS%20-%20SPECIALIST%27S%20FACTUAL%20REPORT-Rel.pdf
- Attachment 1 to engine data monitors - specialist's factual report (item 17, CSV, 56 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16367961&FileExtension=csv&FileName=ATTACHMENT%201%20TO%20ENGINE%20DATA%20MONITORS%20-%20SPECIALISTS%20FACTUAL%20REPORT-Rel.csv
- N304MA - most recent weight and balance sheet (item 18, PDF, 1 page, 42.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17059064&FileExtension=pdf&FileName=N304MA%20-%20Most%20Recent%20Weight%20and%20Balance%20Sheet_Redacted-Rel.pdf
- Mooney - M20K airplane flight manual, emergency procedures excerpts (item 19, PDF, 5 pages, 906 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17063398&FileExtension=pdf&FileName=Mooney%20M20K%20Airplane%20Flight%20Manual%20-%20Emergency%20Procedures%20Excerpts-Rel.pdf
- Continental motors - mandatory service bulletin 94-8D magneto to engine timing (item 20, PDF, 7 pages, 152 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17054080&FileExtension=pdf&FileName=Continental%20Motors%20MSB94-8D%20Magneto%20To%20Engine%20Timing-Rel.pdf
- Release of aircraft wreckage, NTSB form 6120.15 (item 21, PDF, 2 pages, 369 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17056918&FileExtension=pdf&FileName=NTSB%20Wreckage%20Release%20Form%20-%20N304MA_Redacted-Rel.pdf
- NTSB party member forms - Mooney international and hartzell propeller (item 22, PDF, 2 pages, 490 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=17056859&FileExtension=pdf&FileName=NTSB%20Party%20Member%20Forms_Redacted-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.

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