WPR11LA459 · McArthur STEEN SKYBOLT
McArthur STEEN SKYBOLT · Accident: aircraft structural failure while maneuvering
From Caldwell Executive Airport (EUL) to Caldwell Executive Airport (EUL)
Event
- NTSB case
- WPR11LA459
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- Unknown
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
McArthur STEEN SKYBOLT
- Aircraft type
- Mcarthur STEEN SKYBOLT
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N77VW
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Caldwell Executive Airport (EUL), Caldwell, IDTo Caldwell Executive Airport (EUL), Caldwell, ID
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 91: General Aviation
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- Maneuvering · aerobatics
- Defining eventThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Aircraft structural failure
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Substantial
Cause areas
- Aircraft › Aircraft structures
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
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.
Probable cause
Structural failure of the upper left wing during aerobatic flight.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record WPR11LA459
- Event ID
- 20110919X61206
- Case number
- WPR11LA459
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: a67c2da3871de8b6760c28fdb4b57cb8ff76a0b1522365d078160d595a8b8d36; retrieved 2026-09-15T16:45:26.088Z.