WPR09FA234 · Upton Bakeng Duce
Upton Bakeng Duce · Accident: aircraft structural failure while maneuvering
From Ramona Airport (RNM) to Ramona Airport (RNM)
Event
- NTSB case
- WPR09FA234
- 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
- 2 · 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
Upton Bakeng Duce
- Aircraft type
- Upton BAKENG DUCE
- 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
- N86YP
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Ramona Airport (RNM), Ramona, CATo Ramona Airport (RNM), Ramona, CA
- 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
- 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 oper/perf/capability
- Aircraft › Aircraft structures
- Organizational issues › Development
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
The pilot and pilot-rated passenger departed for a personal flight in the borrowed experimental amateur-built airplane, which was equipped with dual flight controls. No determination could be made regarding which occupant was handling the controls during the flight. Recorded radar data indicated that 11 minutes into the flight, a series of maneuvers were performed. A witness stated that he observed the accident airplane spiral downward until it impacted the ground. He also reported observing a wing, which was separated from the main body of the airplane, fall to the ground nearby. Right wing spar fragments and the right aileron were found between 0.1 and 0.3 mile from the main wreckage, indicating that the right wing had separated in flight.
Postaccident examination of fragments from the right wing’s broken wood wing spar revealed that the spar had been constructed with a wood grain orientation 12 degrees from the spar's longitudinal axis. This angle was inconsistent with published Federal Aviation Administration (FAA) guidance stating that grain deviation from the longitudinal axis of the spar should be no more than 3.8 degrees. The maximum grain deviation is limited because the relative strength and stiffness of an airplane’s wood wing spar is reduced when the grain structure within the spar is not oriented parallel to the longitudinal axis of the spar. With a 12-degree grain orientation, the spar’s load-carrying capability was compromised and reduced to between 30 to 70 percent of that of a spar with a 0-degree (parallel) grain orientation. It is likely that the wing spar failed when the pilot performed a maneuver that produced aerodynamic loads exceeding its degraded strength.
Probable cause
An in-flight separation of the right wing, which resulted from the pilot's performance of a maneuver that produced aerodynamic loads that exceeded the wing spar’s degraded strength. The wing spar strength degradation was due to the builder's failure to comply with Federal Aviation Administration recommended guidelines to select and incorporate wood in the spar with a grain pattern aligned with the longitudinal axis of the spar.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record WPR09FA234
- Event ID
- 20090509X02427
- Case number
- WPR09FA234
- 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: b88fa00d3a971d3699fcbaebcba74b64c0d651e6d2700d51bc290b9237d7472f; retrieved 2026-09-13T20:06:53.934Z.