Ramona, CA, USA
N86YP
Upton Bakeng Duce
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.
HISTORY OF FLIGHT On May 9, 2009, about 1435, an Upton Bakeng Duce, N86YP, experienced an in-flight breakup while maneuvering, followed by an uncontrolled descent into an open field, about 6.4 miles east-southeast of Ramona, California. The private pilot, who borrowed the airplane from its owner, occupied the rear seat of the experimental, single engine, airplane. The pilot, who occupied the front seat, held a commercial pilot certificate. The airplane sustained substantial damage to the structure, which was extensively fragmented. There was no fire. Both pilots were killed during the personal flight. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight was performed under the provisions of 14 Code of Federal Regulations Part 91, and it originated from the Ramona airport about 1424. Federal Aviation Administration (FAA) and National Transportation Safety Board personnel interviewed a total of nine persons who reported observing and/or hearing the accident. One of these witnesses reported to the Safety Board investigator that, from her vantage point on elevated terrain in a hilly area, she had observed two airplanes flying in close proximity to each other for at least several minutes prior to their colliding. According to this witness, one of the airplanes was flying slower than the other airplane. The faster moving airplane was predominantly white in color, and the slower moving airplane was predominantly colored red. (The accident airplane’s fuselage was red; its wings were white.) The witness further reported to the Safety Board investigator that she observed the airplanes maneuvering "dangerously" close to each other. The witness stated that during the time she observed these airplanes, the red airplane appeared to make relatively shallow bank turns as compared with the maneuvers that the white airplane performed. The airplanes appeared to have collided while the red airplane was flying in an easterly direction, and the unidentified airplane was climbing in a northerly direction. The witness reported that an instant following what appeared to have been the midair collision she yelled out “The white airplane hit the red airplane.” The witness additionally reported that, immediately following the collision, the red airplane rolled into a 90-degree bank, a span of wing appeared to break off, and the airplane spiraled downward until impacting the ground. Following the impact, she did not recall seeing the faster airplane again. Eight other witnesses made statements indicating that they heard a sputtering engine and looked upward. One of the witnesses stated that he observed the accident airplane spiral downward until it made a dull thud upon impacting the ground. He also reported observing a wing, which was separated from the main body of the airplane. Another of the witnesses stated he observed a large piece of the airplane that looked like a parallelogram fluttering as it fell. None of these witnesses reported observing a second airplane flying in the vicinity at the time of the crash. Radar Track Examination Safety Board and FAA air traffic control personnel examined recorded radar from all of the pertinent radar site locations that had coverage in the hilly terrain that surrounds the crash site and in the neighboring vicinity. Radar coverage of primary (non-transponder) equipped aircraft in the accident site area was problematic at elevations below 1,000 feet above ground level. Primary radar targets were found for an aircraft that departed the Ramona Airport area about 1425, and then tracked southeast toward the accident location. The last target was detected about 1435, approximately 1/4 mile from the crash site. The aircraft appears to have begun executing various course changes in the area of the accident site commencing about 1432. According to the Safety Board’s air traffic control investigator, the radar data appears to show only one aircraft in the vicinity. No altitude information was available for the aircraft. The witness statement regarding the presence of a second aircraft and a possible midair collision could not be substantiated by radar observations. PERSONNEL INFORMATION The 60-year-old pilot who occupied the airplane’s rear seat held a private pilot certificate with a single engine land airplane rating. He also held an airframe and powerplant mechanic certificate. In January, 2008, the pilot reported having 1,450 hours of flight time when he was issued a second-class aviation medical certificate with the limitation that he wear corrective lenses. The 50-year-old pilot who occupied the airplane’s front seat held a commercial pilot certificate with ratings for glider, single engine land airplane, and instrument airplane. He also held a certified flight instructor certificate for single engine land airplanes that expired in 1990. The pilot also held a control tower operator certificate. In December 2008, the pilot reported having 1,050 hours of flight time when he was issued a second-class aviation medical certificate with the limitation that he wear corrective lenses. AIRCRAFT INFORMATION In 1986, the FAA issued the airplane’s builder operating limitations for the airplane and an airworthiness certificate. In part, the limitations stated that operators of the airplane were prohibited from aerobatic flight, which is an intentional maneuver involving an abrupt change in attitude, an abnormal attitude, or abnormal acceleration, not necessary for normal flight. FAA records indicate that the experimental, amateur built, single-engine airplane was manufactured by Samuel L. Upton. The airplane model was called a Bakeng Duce, and it bore serial number 572. The airplane was equipped with a 140-horsepower, Lycoming O-290D engine that was installed in the airplane’s wood frame structure. The airplane was equipped with two seats, in a tandem configuration, and dual flight controls. The airplane could be flown from either seat. According to the airplane’s owner, the pilot in the rear seat was the FAA certificated mechanic who performed a conditional (annual) inspection on the airplane on May 2, 2009, at a total airframe time of 480 hours. Although the airplane is equipped with dual flight controls, the rear seat’s instrument panel contains more instruments, including circuit breakers, than the front seat’s panel. METEOROLOGICAL INFORMATION Witnesses located within less than 1 mile from the accident site reported that the sky condition was clear, and the wind was light and variable. The visibility was not restricted. Ramona Airport is located about 8 miles west of the accident site. At 1453, it reported having a clear sky with 10 miles visibility. WRECKAGE AND IMPACT INFORMATION The main wreckage was located in an open, near level, field at the following global positioning system coordinates: 32 degrees 59.319 minutes north latitude by 116 degrees 46.969 minutes west longitude. The field elevation was about 1,840 feet mean sea level (msl). FAA and airplane recovery personnel reported finding fragmented airplane parts in the field, between 0.1 and 0.3 miles east-northeast of the main wreckage. The airplane’s owner reported that his Bakeng Duce was destroyed upon impacting the ground and fragmenting into numerous pieces. Photographs provided by the FAA indicated that the airplane came to rest on its right side. The entire empennage was attached to the fuselage. The cockpit was crushed and fragmented. The metal propeller and engine assembly were found together, adjacent to the firewall and main wreckage. Both wings were crushed, with multiple breaks observed in the forward and aft spars. The wings were broken from both their fuselage attachment points, and from their lift struts, which were bent. No evidence of fire or oil residue was observed on the empennage. Safety Board personnel examined the airplane wreckage following its recovery. The flight control continuity to the rudder and elevator assembly was confirmed from the aft fuselage to the respective control surfaces. The entire left wing spar was located, although it was broken in several locations. The left wing’s aileron was found attached to the wing. The control cable continuity to the left wing’s aileron was confirmed from the aileron to the fuselage. The right wing spar was found fragmented in numerous locations, mostly outboard of the location where the wing lift strut attaches to the wing. The right wing’s aileron was found separated from the wing. Reportedly, it had been located about 0.1 mile east of the main wreckage, in the vicinity of numerous wood fragments. An examination of the white colored left and right wing skin did not disclose any visible evidence of a colored paint transfer onto the skin. The painted skin exhibited numerous scratch marks and tears oriented in various directions. Not all pieces of skin were located. MEDICAL AND PATHOLOGICAL INFORMATION Autopsies were performed on the pilots by the County of San Diego, California, Office of the Medical Examiner. The reports indicate that the cause of death for both pilots was multiple blunt force injuries. The Medical Examiner and the FAA’s Civil Aerospace Medical Institute, Oklahoma City, Oklahoma, performed forensic toxicology on specimens from the pilots. No evidence of ethanol or drugs of abuse were detected. TESTS AND RESEARCH Wood Spar Construction and Laboratory Examination Several of the fractured and separated right wing spar segments (outboard of the lift strut-to-wing attachment point) were submitted to the Safety Board for analysis by the Office of Research and Engineering, Materials Laboratory, Washington, D.C. In pertinent part, the laboratory’s examination of fractured right wing spar components revealed that the fractures at the inboard and outboard ends of one fragmented forward spar piece occurred primarily as splits along the grain of the wood. The splitting fracture indicated that the grain of the wood was not aligned with the longitudinal axis of the spar. An examination of one sample indicated that the average angle of deviation between the wood grain and the spar axis was approximately 12 degrees. A 12-degree angle of deviation would correspond to a slope of more than 1 in 5. Laboratory personnel additionally noted that the misaligned wood grain was not apparent by viewing either the front or back surfaces of the spar. Wood strips had been attached to the top and bottom edges of sections of the spar, which precluded one’s ability to observe the misalignment. The effect of the misaligned grain orientation on the spar’s strength was evaluated. According to a United States Department of Agriculture, Forest Products Laboratory General Technical Report, a grain offset angle of 12 degrees predicts that the bending strength decreases to a value between 30 and 70 percent of the strength for a structure with grain aligned with its axis. The FAA’s publication (AC 43.13-1B) entitled “Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair,” states that the maximum permissible grain deviation (slope of grain) is 1 in 15, or 3.8 degrees. The relative strength and stiffness of an airplane’s wood wing spar is reduced when the grain structure within the spar is not oriented in a longitudinal direction, relative to the longitudinal axis of the spar.
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.
Source: NTSB Aviation Accident Database
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