Upton Bakeng Duce — Ramona, CA, 2009

Upton Bakeng Duce — Ramona, CA

2 fatal High-time pilot

Date	May 9, 2009
Location	Ramona, CA
Aircraft	Upton Bakeng Duce (amateur-built)
Purpose of flight	Personal
Conditions	Day · Visual Meteorological Cond
Phase / occurrence	Prior to flight Miscellaneous/other
Pilot age	60
Pilot total time	1,450 hrs · Experienced
Time in type	Unknown
Fatalities	2

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.

NTSB findings

Organizational issues-Development-Manufacture/production-(general)-Manufacturer - C
Aircraft-Aircraft structures-Wing structure-Spar (on wing)-Damaged/degraded - C
Aircraft-Aircraft structures-Wing structure-Spar (on wing)-Failure - C
Aircraft-Aircraft oper/perf/capability-Performance/control parameters-Dynamic load-Capability exceeded - C

What happened

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.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.