Amateur-built S-18 THORP accident near Porterville, California, September 1, 2018
On September 1, 2018 at about 4:10 pm local time, a 2007 amateur-built S-18 THORP, registered N575DG, was substantially damaged in an accident during takeoff near Porterville, California (Porterville Muni airport). It was a personal flight under general aviation rules (Part 91). 1 person had minor injuries. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The pilot’s failure to maintain directional control during the takeoff roll.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- September 1, 2018 · about 4:10 pm local time
- Place
- Porterville, California · Porterville Muni · map
- Type
- Accident
- Injuries
- 1 person had minor injuries.
- Weather
- visual conditions (good weather)
- Aircraft
- Amateur-built S-18 THORP, built 2007
- Registration
- N575DG · registry record · serial 218
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The pilot of the tailwheel-equipped airplane reported that, during takeoff, he advanced the throttle to full power, maintained the runway centerline, and began to raise the tail. He added that, about 60 mph, the airplane suddenly turned left. He applied full right rudder to no avail. Subsequently, the airplane continued to veer left, exited the runway into plowed dirt, and nosed over. The airplane sustained substantial damage to the fuselage and vertical stabilizer. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. The automated weather observation system at the airport reported that, about the time of the accident, the wind was variable at 3 knots. The pilot was departing from runway 30.
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 takeoff defining event
- Attempted remediation/recovery during takeoff
- Runway excursion during takeoff
- Nose over/nose down during takeoff
The NTSB's findings
- cause Aircraft › Aircraft oper/perf/capability › Performance/control parameters › Directional control › Not attained/maintained
- cause Personnel issues › Task performance › Use of equip/info › Aircraft control › Pilot
- Environmental issues › Physical environment › Terrain › Rough terrain › Contributed to outcome
Pilot
- Certificate: private
- Ratings: single-engine land; instrument: airplane
- Flight time: 209 hours in all; 12 in this make and model; 18 in the last 90 days; 7 in the last 30 days; 160 as pilot in command
- Last flight review: June 28, 2017
- Medical certificate: Class 1 (without waivers/limitations)
- Seat: left
- Injury: minor injuries
The aircraft
- Airframe total time: 348.4 hours
- Last inspection: condition inspection, July 21, 2018
- Maximum gross weight: 1,600 lb
- Seats: 2
- Landing gear: fixed
- Engine: Lycoming O-320-E2D (piston); 2,439 hours total
The flight
- Departed from: O42 Woodlake CA at 3:20 pm
- Destination: PTV Porterville CA
- Flight plan: none
- Runway 30, 5,960 ft by 150 ft
Weather at the time
- Light: daylight
- Visibility: 8 statute miles
- Sky: clear
- Temperature: 75°F (24°C), dew point 59°F (15°C)
- Altimeter: 29.89 inHg
- Observation at 4:56 pm from KPTV
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
1 document, released by the NTSB on November 6, 2018. 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, 11 pages | View Download |
The same docket at the NTSB · documents without a copy here are fetched from the NTSB when you open them.
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.