Amateur-built STEEN SKYBOLT accident near Greenleaf, Idaho, September 19, 2011
On September 19, 2011 at about 7:15 pm local time, a amateur-built STEEN SKYBOLT, registered N77VW, was substantially damaged in an accident during maneuvering (aerobatics) near Greenleaf, Idaho (Caldwell 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
Structural failure of the upper left wing during aerobatic flight.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- September 19, 2011 · about 7:15 pm local time
- Place
- Greenleaf, Idaho · Caldwell · map
- Type
- Accident
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Amateur-built STEEN SKYBOLT
- Registration
- N77VW · no longer on the register · serial 1
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The pilot was performing aerobatic maneuvers in the plans-built experimental biplane. He successfully completed an aerobatic routine and then elected to perform it a second time. During the initial dive, as he began to level the airplane, he observed the outboard trailing edge of the upper left wing fail, with fabric material in trail from the aft spar. He regained partial control, but decided to bail out a short time later. The airplane subsequently rolled inverted and entered a near-vertical descent that continued to ground impact. The 15-year-old airplane, which was purchased by the pilot 16 months before the accident, had fabric-covered wooden wings. The pilot described the build quality of the airplane as "average" and stated that he had noted chips and cracks in the paint, which were acceptable when referenced to the inspection criteria in the fabric manufacturer’s installation manual. The airplane sustained extensive impact damage, and sections of the upper left wing separated from the airframe in flight and were not located. Fabric material from the recovered wreckage was examined, and the paint was cracked, fragmented, and separated from the majority of the fabric surface. It appeared that the fabric had been incorrectly treated prior to painting and then painted with a brittle automotive paint, which was prone to cracking. The fabric manufacturer’s installation manual cautioned that automotive paint can lead to premature failure of fabric cover because cracking can expose the fabric material to damaging ultraviolet light, which will substantially reduce the fabric's strength. The failed area was on the upper wing, which would have been exposed to sunlight on a regular basis. Although the improperly treated and painted fabric may have led to the in-flight failure of the upper left wing, a determination of the wing’s failure mode could not be made because the separated section of the wing was not recovered.
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
- Aircraft structural failure during maneuvering (aerobatics) defining event
- Attempted remediation/recovery during maneuvering (aerobatics)
- Collision with terrain or object (not controlled flight into terrain) during uncontrolled descent
The NTSB's findings
- cause Aircraft › Aircraft structures › Wing structure › Flight surfaces (wing) › Failure
- Personnel issues › Task performance › Maintenance › Installation › Other/unknown
- Aircraft › Aircraft structures › Wing structure › Plates/skins (on wing) › Incorrect service/maintenance
Pilot
- Certificate: airline transport pilot
- Ratings: multi-engine land; single-engine land; instrument: airplane
- Flight time: 14,405 hours in all; 58 in this make and model; 205 in the last 90 days; 73 in the last 30 days; 10,997 as pilot in command; 929 on instruments
- Last flight review: July 25, 2011
- Medical certificate: Class 1 (without waivers/limitations)
- Seat: rear
- Injury: no injuries
The aircraft
- Airframe total time: 320 hours
- Last inspection: condition inspection, September 3, 2011; 4 hours since
- Maximum gross weight: 1,800 lb
- Seats: 2
- Landing gear: fixed
- Engine: Lycoming IO-360 (piston); 0 hours total
The flight
- Departed from: EUL Caldwell ID at 6:55 pm
- Destination: EUL Caldwell ID
- Flight plan: none
Weather at the time
- Light: daylight
- Wind: from 330° at 5 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 75°F (24°C), dew point 45°F (7°C)
- Altimeter: 30.11 inHg
- Observation at 6:55 pm from EUL, 9 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
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.