Helio H-391B accident near Monroe, Michigan, August 18, 2025
On August 18, 2025 at about 5:30 pm local time, a 1958 Helio H-391B, registered N4431U, was substantially damaged in an accident during landing (flare/touchdown) near Monroe, Michigan (Custer 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
The pilot’s failure to maintain directional control during the landing roll with a crosswind.
Source: NTSB aviation accident database, copy made October 4, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- August 18, 2025 · about 5:30 pm local time
- Place
- Monroe, Michigan · Custer Airport · map
- Type
- Accident
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Helio H-391B, built 1958 · all H-391Bs on the register
- Registration
- N4431U · registry record · serial 091
- 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 while landing his tailwheel airplane in a crosswind, the airplane bounced upon touchdown. The right wing lifted, the airplane drifted down the runway on the left wheel, and the airplane exited the runway into the grass. The left wheel dug into the grass and the airplane pivoted. During the accident sequence, the left landing gear separated from the fuselage, and the left wing struck the ground. The left wing was substantially damaged. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. At the time of the accident, the pilot was landing the airplane on runway 03 with wind from 100° at 10 knots gusting 15 knots.
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 control on ground during landing (flare/touchdown) defining event
- Other weather encounter during landing (landing roll)
- Runway excursion during landing (landing roll)
The NTSB's findings
- Personnel issues › Task performance › Use of equip/info › Aircraft control › Pilot
- Aircraft › Aircraft oper/perf/capability › Performance/control parameters › Directional control › Not attained/maintained
- Environmental issues › Conditions/weather/phenomena › Wind › Crosswind › Effect on operation
Pilot
- Certificate: private
- Ratings: single-engine land
- Flight time: 329 hours in all; 12 in this make and model; 12 in the last 90 days; 12 in the last 30 days
- Last flight review: September 13, 2024
- Medical certificate: Class 3 (with waivers/limitations)
- Seat: left
- Injury: no injuries
The aircraft
- Airframe total time: 2,385 hours
- Last inspection: annual inspection, August 8, 2025; 14 hours since
- Maximum gross weight: 3,000 lb
- Seats: 4
- Landing gear: fixed
- Engine: Lycoming GO435C2B2-6 (piston); 0 hours total
The flight
- Departed from: 3NP Napolean MI at 5:00 pm
- Destination: TTF Monroe MI
- Flight plan: none
- Runway 03, 4,997 ft by 100 ft
Weather at the time
- Light: daylight
- Wind: from 100° at 10 knots, gusting 15
- Visibility: 10 statute miles
- Sky: broken clouds at 3,200 ft
- Temperature: 75°F (24°C), dew point 63°F (17°C)
- Altimeter: 30.18 inHg
- Observation at 1:35 pm from KTTF
Weather report (METAR): KTTF 181735Z AUTO 10010G15KT 070V130 10SM BKN032 OVC038 24/17 A3018
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 January 9, 2026. 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 | Photos | PDF, 4 pages | 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 N4431U the same tail number, which may have belonged to a different aircraft at the time
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 documents and photographs are the NTSB's docket, the folder of records gathered during the investigation, shown as the NTSB released them (the NTSB redacts some personal details first) and listed under the NTSB's own titles. This site's own text 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 CEN25LA325.