Upton BAKENG DUCE N86YP

Summary

On 9 May 2009 at about 21:35 local time, a Upton BAKENG DUCE registered N86YP was involved in an accident near Ramona, California, United States. 2 people were on board and 2 died. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

9 May 2009 at 21:35

Classification

Accident

Location

Ramona, California, United States

Nearest airport

Ramona (RNM)

Coordinates

32.9886, -116.7819

Aircraft

Upton BAKENG DUCE

Registration

N86YP

Category

Airplane

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Ramona → Ramona

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

WPR09FA234

2 people died.

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.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full 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.

Quoted verbatim from the NTSB record.