HISTORY OF FLIGHTOn June 15, 2012, about 1940 mountain daylight time, an experimental amateur-built Roetman Eagle, N106BD, was substantially damaged when it impacted terrain while conducting aerobatic maneuvers at the Rexburg-Madison County Airport (RXE), Rexburg, Idaho. The pilot/owner sustained serious injuries, and there were no ground injuries. The airplane was being operated under the provision of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed for the local area flight, and no flight plan had been filed.
The flight originated at RXE, and the pilot was practicing for an upcoming airshow at that airport. The airplane was recovered for potential further examination. PERSONNEL INFORMATIONFederal Aviation Administration (FAA) records indicated that the pilot held airline transport and flight instructor certificates, with multiple ratings, and a mechanic certificate with airframe and powerplant ratings.
According to information provided by the pilot, he had approximately 14,223 total hours of flight experience, including approximately 1,500 hours in the accident airplane make and model. His most recent flight review was completed in January 2012, and his most recent FAA first-class medical certificate was issued in May 2012. AIRCRAFT INFORMATIONFAA records indicated that the biplane was built in 2003 by the pilot/owner. It was equipped with a Lycoming IO-360 series engine, and a variable pitch 3-blade MT-9-190 composite propeller. It had an enclosed cockpit, and conventional-style landing gear. METEOROLOGICAL INFORMATIONThe RXE 1953 automated weather observation included wind from 180 degrees at 5 knots, visibility 10 miles, clear skies, temperature 22 degrees Celsius, dew point 1 degree Celsius, and an altimeter setting of 30.00 inches of mercury. AIRPORT INFORMATIONFAA records indicated that the biplane was built in 2003 by the pilot/owner. It was equipped with a Lycoming IO-360 series engine, and a variable pitch 3-blade MT-9-190 composite propeller. It had an enclosed cockpit, and conventional-style landing gear. WRECKAGE AND IMPACT INFORMATIONThe airplane impacted a relatively level grassy area interspersed with a few trees, and was adjacent to the airport. The ground scars extended for a distance of approximately 120 feet.
The airplane came to rest upright. Both right wings sustained significant damage. Both main landing gear were collapsed, and all three blades of the wood/composite propeller were fracture-separated at or near the hub. The propeller hub remained attached to the engine, and the engine remained attached to its mounts. The engine mount and firewall were damaged and partially separated from the airplane. The aft fuselage and empennage were essentially intact, and the cockpit retained its integrity. There was no post impact fire.
Separate examinations of the airplane by FAA and insurance company personnel did not reveal any pre-impact mechanical deficiencies or failures. The NTSB did not conduct any examinations of the wreckage or any components. ADDITIONAL INFORMATIONVideo Imagery
Amateur video footage taken from the ground, with duration of about 18 seconds, captured a portion of the flight and accident sequence. The footage was publicly available on the YouTube website. The video shows the airplane conducting multiple continuous right rolls at an approximately constant altitude, followed by an apparent slowing and descent of the airplane, while still rolling. The airplane maintained a relatively constant pitch attitude during the roll maneuvers, as well as, during both the horizontal and descending segments of the flight. The rolling ceased when the airplane was approximately 100 feet above the ground; however, the airplane continued in its descent in a significant right wing down attitude. The ground impact was mostly obscured from view by terrain. The majority of the footage did not contain any ground or other fixed features, so no trajectory information was able to be derived from the video.
Pilot-Provided Information
In several post-accident conversations with investigation personnel, the pilot provided description information for the airplane, and his opinion as to the cause of the accident.
The engine was equipped with a variable-pitch propeller that was controlled/actuated by a propeller governor, utilizing engine oil and engine oil pressure.
Occasionally, during certain aerobatic maneuvers, the engine oil pressure would decrease due to the loads and/or attitudes of those maneuvers. That decrease in oil pressure during those maneuvers sometimes resulted in uncommanded (by the pilot) and undesired propeller blade pitch increases (blades moving towards coarse pitch or feather position). About 4 years prior to the accident, the pilot installed an accumulator in the governor supply side oil line, in order to reduce or eliminate those occasional oil pressure drops from adversely affecting propeller blade pitch. The pilot did not install any gauges to indicate the pre-charge pressure in the accumulator, or any warning lights to signal a loss of accumulator pre-charge. The pilot reported that the accumulator system had performed reliably since its installation.
The pilot did not check the accumulator pre-charge pressure prior to any flight; in his experience, the system was sufficiently robust and reliable that the pre-charge was only checked during annual or other detailed inspections.
While conducting the maneuver, just prior to the accident, the pilot "heard and felt" an uncommanded propeller rpm decrease. He concluded that the rpm loss was due to the expected decrease in engine oil pressure (from the maneuver), and the failure of the accumulator to provide sufficient oil pressure to prevent the propeller blades from increasing in pitch. The pilot also concluded that the accumulator failure was due to its loss of some or all of its pre-charge pressure. The pilot did not provide any basis for that assessment/conclusion. FLIGHT RECORDERSThe airplane was equipped with a "Drift HD" recorder. The device was a portable, all-in-one recording unit utilizing a 170-degree lens, capable of recording high definition still and video images, and audio. The unit records to a removable micro SD card. The device was sent to the NTSB recorders laboratory in Washington, D.C., for readout. The SD card did not contain any data related to the accident flight.