# NTSB CEN24LA141: Cozy Mark IV, N20MN, Gonzales, TX, March 25, 2024 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: March 25, 2024, 18:53 local (23:53 UTC) - Place: Gonzales, TX · Grassy area adjacent to a runway - Coordinates: 29.532729, -97.46641 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=29.5327&lon=-97.4664&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report April 3, 2026 - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Central Region - Parties: FAA/FSDO - NTSB case key (mKey): 193992 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN24LA141 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193992/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=193992 - Page: https://openairdocs.org/ntsb/CEN24LA141 ## Probable cause Maintenance personnel’s failure to properly torque the crankshaft idler gear hardware according to the engine manufacturer’s service instructions, which resulted in separation of the crankshaft idler gear’s fasteners and disengagement of the camshaft, crankshaft, and crankshaft idler gear and a subsequent total loss of engine power. ## 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 · Related maintenance info (probable cause); cases with it: [Parmelee M/Parmelee N COZY MARK IV, 1 case](https://openairdocs.org/ntsb-findings/01058540/cases.md?model=05607XT), [All aircraft, 42 cases](https://openairdocs.org/ntsb-findings/01058540/cases.md) - [Engine (reciprocating): recip eng rear section](https://openairdocs.org/ntsb-findings/01058540): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Parmelee M/Parmelee N COZY MARK IV, 1 case](https://openairdocs.org/ntsb-findings/01058540/cases.md?model=05607XT), [All aircraft, 42 cases](https://openairdocs.org/ntsb-findings/01058540/cases.md) - [Maintenance](https://openairdocs.org/ntsb-findings/02062000): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Parmelee M/Parmelee N COZY MARK IV, 1 case](https://openairdocs.org/ntsb-findings/02062000/cases.md?model=05607XT), [All aircraft, 143 cases](https://openairdocs.org/ntsb-findings/02062000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Parmelee M/Parmelee N COZY MARK IV, 1 case](https://openairdocs.org/ntsb-events/341/sequence.md?model=05607XT), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Emergency descent: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Parmelee M/Parmelee N COZY MARK IV, 1 case](https://openairdocs.org/ntsb-events/440/sequence.md?model=05607XT), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing: Landing area undershoot](https://openairdocs.org/ntsb-events/370); cases with it: [Parmelee M/Parmelee N COZY MARK IV, 1 case](https://openairdocs.org/ntsb-events/370/sequence.md?model=05607XT), [All aircraft, 201 cases](https://openairdocs.org/ntsb-events/370/sequence.md) ## Analysis While enroute, at 9,500 ft above mean sea level (msl), the engine lost all power. After multiple attempts to restart the engine, the pilot executed a forced landing to a nearby airport. The airplane landed short of the runway threshold and its nose landing gear separated as the airplane transitioned onto the asphalt runway. The left wing and left canard sustained substantial damage. Postaccident examination of the engine revealed that the left crankshaft idler gear shaft separated from its attach points, which prevented the crankshaft idler gear from engaging its corresponding crankshaft and camshaft gears. The disengagement prevented camshaft rotation and valvetrain timing to the crankshaft. The left crankshaft idler gear’s attachment hardware were both separated into two sections from abrasion. The capscrew was lockwired to the idler shaft but no lockwire was observed through the stud and slotted shear nut. It is likely that maintenance personnel did not follow the engine manufacturer’s service instructions and undertorqued the fasteners during installation, resulting in insufficient clamping force. Additionally, the absence of lockwire likely permitted the shear nut to back off during engine operation. Because the airplane’s maintenance records were not available for review, the investigation was not able to identify when the crankshaft idler gear was last serviced. ## Factual narrative On March 25, 2024, about 1853 central daylight time, a Cozy Mark IV airplane, N20MN, was substantially damaged when it was involved in an accident near Gonzales, Texas. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that while enroute, about 9,500 ft msl, the airplane sustained a total loss of engine power. After multiple attempts to restart the engine, the pilot executed a forced landing to a nearby airport. The airplane landed short of the runway threshold and its nose landing gear separated as the airplane transitioned onto the asphalt runway. The left wing and left canard sustained substantial damage. Postaccident examination of the engine revealed there was no valvetrain continuity when the engine was rotated through at the propeller. Further examination revealed the left crankshaft idler gear was disengaged from the crankshaft and camshaft gears. The 5/16-inch stud, slotted shear nut, and capscrew fasteners that attached the crankshaft idler gear shaft to the crankcase were abraded and separated into two sections. The capscrew was lockwired to the idler shaft but no lockwire was observed through the stud and slotted shear nut and there were no separated sections of lockwire observed in the oil sump. Abrasion was noted to the heads of the cap screw and slotted shear nut. Additionally, circular abrasion observed to the back of the crankshaft idler gear was consistent with the fasteners contacting the idler gear during engine operation. The idler shaft recess in the crankcase exhibited deformation and abrasion. The idler gear shaft contained a bushing that was consistent with the Lycoming Engine’s Service Instruction No. 1197A, Repair of Idler Gear Shaft Recesses, dated March 29, 1974. The bushing was fractured in two sections and deformed. According to the Lycoming Engine’s Service Instruction No. 1310A, Lockwire for Idler Shafts, dated February 25, 1977, the required capscrew torque is 200-inch pounds and the slotted shear nut torque is 150-inch pounds. Additionally, it requires both fasteners to be lockwired. The pilot’s flight logs and airplane maintenance records were not made available during the course of the investigation. Additionally, the pilot did not submit the Pilot/Operator Aircraft Accident/Incident Report Form despite multiple requests. ## Aircraft - Registration: [N20MN](https://openairdocs.org/aircraft/N20MN), registered now, S/N 425, built 1999 (OpenAirDocs) - Reported make and model: Cozy Mark IV - Registry model: [Parmelee M/Parmelee N COZY MARK IV](https://openairdocs.org/model/parmelee-m-parmelee-n-cozy-mark-iv) (registry code 05607XT) (OpenAirDocs) - Registry engine: [Lycoming 0-360-A1D](https://openairdocs.org/engine/lycoming-0-360-a1d) (registry code 41504, reciprocating) (OpenAirDocs) - Category: Airplane, amateur-built - Serial number: 425 - Year built: 1999 - Airframe hours: 1464 - Engines: Lycoming O-360-A3A 180 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Unknown, October 17, 2023, 43.6 hours before - Departed: SSF, San Antonio, TX - Destination: EFD, Houston, TX - Airport: T20, Roger M. Dreyer Memorial Airport, runway 33, 3,200 × 50 ft, asphalt - Equipment: Electronic multifunction display, ADS-B, Electronic primary flight display ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 53; injuries: none; private; airplane ratings: single-engine land; medical: basicmed, unknown; seat: left ## Weather - Conditions: Visual (VMC), Day - Wind: 300° at 12 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 77 °F, dew point 34 °F - Altimeter: 29.54 inHg - Observed at: BAZ, 32 nm away - METAR: KBAZ 252351Z AUTO 30012KT 10SM CLR 25/01 A2954 RMK AO2 SLP998 T02500011 10267 20244 53008 PWINO $ ## 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 20240325005209A](https://openairdocs.org/incident/20240325005209A), Mar 25, 2024: Parmelee M/Parmelee N COZY MARK IV, Gonzales, TX, Substantial damage. On 03/25/2024, the pilot of the accident aircraft contacted san antonio ATC declaring an emergency due to loss of engine. He advised ATC that he would attempt… ## Docket (6 files) The files NTSB released with the investigation on April 3, 2026, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=193992. 4.8 MB in all. - Mor pilot statement (item 1, PDF, 1 page, 69 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19911974&FileExtension=pdf&FileName=MOR%20Pilot%20Statement_Redacted-Rel.pdf - Mor NTSB 6120 1 and 6120 15A forms correspondence (item 2, PDF, 1 page, 65 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19913358&FileExtension=pdf&FileName=MOR%20NTSB%206120%201%20and%206120%2015a%20Forms-Rel.pdf - NTSB examination summary (item 3, PDF, 5 pages, 205 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19914967&FileExtension=pdf&FileName=Engine%20Examination%20Summary-Rel.pdf - Photo array (item 4, PDF, 4 pages, 945 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19912510&FileExtension=pdf&FileName=Photo%20Array-Rel.pdf - Lycoming publications (item 5, PDF, 10 pages, 3.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19912670&FileExtension=pdf&FileName=Lycoming%20Publications-Rel.pdf - Release of aircraft wreckage, NTSB form 6120.15 (item 6, PDF, 1 page, 113 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=19911777&FileExtension=pdf&FileName=Wreckage%20Release%20Form_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. --- 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.