Stemme GMBH & CO S10-VT accident near Mackinaw City, Michigan, August 31, 2013
On August 31, 2013 at about 1:15 am local time, a 2001 Stemme GMBH & CO S10-VT (glider), registered N389BD, was substantially damaged in an accident during approach (VFR pattern final) near Mackinaw City, Michigan. It was a personal flight under general aviation rules (Part 91). 1 person was seriously injured; 1 other was unhurt. The weather was visual conditions (good weather).
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The NTSB's probable cause their words, unchanged
The mechanic’s failure to inspect the tightness of the bolts that connected the flexible disk to the driveshaft, which resulted in the failure of these components.
Source: NTSB aviation accident database, copy made October 4, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- August 31, 2013 · about 1:15 am local time
- Place
- Mackinaw City, Michigan · map
- Type
- Accident
- Injuries
- 1 person was seriously injured; 1 other was unhurt.
- Weather
- visual conditions (good weather)
- Aircraft
- Stemme GMBH & CO S10-VT, built 2001 · all S10-VTs on the register
- Registration
- N389BD · no longer on the register · serial 11-066
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The pilot reported that the motor-glider was on a long, straight-in visual approach to land when he heard a very loud "bang" in the front of the motor-glider followed by a severe vibration. The pilot shut down the engine and made a forced landing to a field. A postaccident examination of the aircraft revealed that the flexible disk on the front of the driveshaft had disconnected. Only one of the three bolts that connected the disk to the driveshaft remained partially installed. No evidence of Loctite or torque paint was found on the bolt. The bolt's threads were rusted, and the bolt's head was digging into the gearbox housing. The second bolt was sheared off, and the third bolt was missing. A review of maintenance records revealed that the motor-glider's most recent annual inspection was completed about 1 month before the accident. According to the manufacturer's maintenance manual, a mechanic was required to check the tightness of the bolt connections of the flexible disk on the front side of the drive shaft. It is likely that the mechanic improperly inspected the bolts that connected the flexible joint to the front side of the driveshaft during the last annual inspection, which resulted in the ultimate failure of these components. The maintenance records also revealed that, during the last annual inspection, Federal Aviation Administration Airworthiness Directive (AD) 2006-19-08, which required inspection for deformations and cracks in the exhaust pipes and the replacement of any damaged exhaust pipes found, had not been properly complied with when a weld repair was made to the No. 1 exhaust pipe. The mechanic's failure to not properly comply with the AD and the operator's failure to ensure that the AD was complied with were not causal to the accident; however, because the AD was not complied with, the motor-glider was not considered airworthy.
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
- Sys/Comp malf/fail (non-power) during approach (VFR pattern final) defining event
- Collision with terrain or object (not controlled flight into terrain) during emergency descent
The NTSB's findings
- cause Aircraft › Aircraft propeller/rotor › (general) › (general) › Failure
- cause Aircraft › Aircraft propeller/rotor › (general) › (general) › Incorrect service/maintenance
- cause Personnel issues › Task performance › Maintenance › Scheduled/routine maintenance › Maintenance personnel
Pilot
- Certificate: private
- Ratings: single-engine land; rotorcraft: glider
- Flight time: 1,200 hours in all; 650 in this make and model; 30 in the last 90 days
- Medical certificate: None
- Seat: left
- Injury: serious injuries
The aircraft
- Airframe total time: 600 hours
- Last inspection: annual inspection, July 20, 2013
- Seats: 2
- Landing gear: retractable
- Engine: (piston); 0 hours total
- Operator: 512 Horses INC
The flight
- Departed from: UGN Waukegan IL at 8:00 pm
- Destination: 5Y1 Hessel MI
- Flight plan: none
Weather at the time
- Light: dusk
- Wind: from 005° at 10 knots
- Visibility: 20 statute miles
- Temperature: 75°F (24°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flig | 1 | |||
| Passengers | 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 CEN13LA524.