Amateur-built Mini 500 accident near Butler, Missouri, August 21, 2015
On August 21, 2015 at about 4:00 pm local time, a 2015 amateur-built Mini 500 (helicopter), registered UNREG, was substantially damaged in an accident during enroute (cruise) near Butler, Missouri (Butler Memorial 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).
The NTSB's probable cause their words, unchanged
The pilot's failure to attain a proper landing flare following an autorotation for reasons that could not be determined based on available information.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- August 21, 2015 · about 4:00 pm local time
- Place
- Butler, Missouri · Butler Memorial · map
- Type
- Accident
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Amateur-built Mini 500, built 2015
- Registration
- UNREG · no longer on the register · serial 001
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The private pilot had just departed the airport in the unregistered, amateur-built helicopter. While in the traffic pattern, the helicopter shuddered and made a noise the pilot described as sounding like a tire blowing out on a car. He performed an autorotation to a soybean field and leveled the helicopter at 5 ft above the ground (2 ft above the crop), although he stated that he believed that the helicopter's tail rotor may have been in the crop, which caused instability. When the rotor speed bled off, the helicopter settled onto its right skid and rolled over. Postaccident examination did not reveal any preimpact anomalies, but a complete examination was not performed. Although the pilot believed that the one-way clutch, part of the power transmission system of the helicopter, had failed, which would have resulted in a loss of power to the rotor system, he had not disassembled the transmission to verify this. Additionally, the pilot's improper flare during the autorotation resulted in a premature loss of rotor speed, and the subsequent rollover.
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 enroute (cruise) defining event
- Autorotation Miscellaneous/other
The NTSB's findings
- cause Aircraft › Aircraft propeller/rotor › Main rotor drive › Engine/transmission coupling › Failure
- cause Aircraft › Aircraft oper/perf/capability › Performance/control parameters › Landing flare › Not attained/maintained
Pilot
- Certificate: private
- Ratings: single-engine land
- Flight time: 300 hours in all; 30 in this make and model; 30 in the last 30 days; 300 as pilot in command
- Last flight review: September 15, 2013
- Medical certificate: Class 3 (without waivers/limitations)
- Seat: sngl
- Injury: no injuries
The aircraft
- Airframe total time: 30 hours
- Last inspection: condition inspection; 30 hours since
- Maximum gross weight: 840 lb
- Seats: 1
- Landing gear: fixed
- Engine: Rotax 582UL (piston); 30 hours total
The flight
- Departed from: BUM Butler MO at 3:50 pm
- Destination: BUM Butler MO
- Flight plan: none
- Runway 18, 3,999 ft by 75 ft
Weather at the time
- Light: daylight
- Wind: from 160° at 10 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 77°F (25°C), dew point 61°F (16°C)
- Altimeter: 30.06 inHg
- Observation at 3:55 pm from GLY, 31 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
2 documents, released by the NTSB on September 22, 2016. View them here, or download them; the NTSB redacts some personal details before release, and this site shows the NTSB's own titles rather than its file names.
| # | Document | What it is | |
|---|---|---|---|
| 1 | Pilot/operator Aircraft Accident Report, NTSB Form 6120.1 | PDF, 10 pages | View Download |
| 2 | Record of Conversation with Pilot | PDF, 1 page | View Download |
The same docket at the NTSB · documents without a copy here are fetched from the NTSB when you open them.
Other NTSB records under UNREG the same tail number, which may have belonged to a different aircraft at the time
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.