Amateur-built Mark IV accident near Gonzales, Texas, March 25, 2024
On March 25, 2024 at about 11:53 pm local time, a 1999 amateur-built Mark IV, registered N20MN, was substantially damaged in an accident during enroute (cruise) near Gonzales, Texas (Roger M. Dreyer Memorial Airpo airport). It was a personal flight under general aviation rules (Part 91). No one was hurt; 1 person was on board or involved. The weather was visual conditions (good weather).
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The NTSB's probable cause their words, unchanged
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.
Source: NTSB aviation accident database, copy made October 4, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- March 25, 2024 · about 11:53 pm local time
- Place
- Gonzales, Texas · Roger M. Dreyer Memorial Airpo · map
- Type
- Accident
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Amateur-built Mark IV, built 1999
- Registration
- N20MN · registry record · serial 425
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
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.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
What happened, in order
- Loss of engine power (total) during enroute (cruise) defining event
- Landing area undershoot during landing
- Off-field or emergency landing during emergency descent
The NTSB's findings
- Aircraft › Aircraft power plant › Engine (reciprocating) › Recip eng rear section › Related maintenance info
- Aircraft › Aircraft power plant › Engine (reciprocating) › Recip eng rear section › Failure
- Personnel issues › Task performance › Maintenance › (general) › Maintenance personnel
Pilot
- Certificate: private
- Ratings: single-engine land
- Medical certificate: BasicMed
- Seat: left
- Injury: no injuries
The aircraft
- Airframe total time: 1,464 hours
- Last inspection: inspection type not recorded, October 17, 2023; 43.6 hours since
- Maximum gross weight: 2,050 lb
- Seats: 3
- Landing gear: retractable
- Engine: Lycoming O-360-A3A (piston); 0 hours total
The flight
- Departed from: SSF San Antonio TX at 11:28 pm
- Destination: EFD Houston TX
- Flight plan: none
- Runway 33, 3,200 ft by 50 ft
Weather at the time
- Light: daylight
- Wind: from 300° at 12 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 77°F (25°C), dew point 34°F (1°C)
- Altimeter: 29.54 inHg
- Observation at 6:51 pm from BAZ, 32 miles away
Weather report (METAR): KBAZ 252351Z AUTO 30012KT 10SM CLR 25/01 A2954 RMK AO2 SLP998 T02500011 10267 20244 53008 PWINO $
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flig | 1 |
About this page
Everything above comes from the NTSB's public accident database: the narrative, probable cause and findings are the NTSB's own words, and the coded tables behind its report (pilot, aircraft, flight, weather, injuries, sequence of events) are written out in plain English. Pilots' ages, home towns and medical details are left out on purpose. The docket at the NTSB holds the report as a PDF and the investigation's photographs and documents. This site never names pilots, passengers or anyone else involved. A preliminary report describes what is known soon after the event and can change; the final report, with the probable cause, usually follows one to two years later and this page is refreshed when it does. Case number CEN24LA141.