History of Flight
On September 20, 2015, at approximately 1706 Pacific daylight time, an experimental amateur-built Bryon S Graves (Vans Aircraft) RV-7A, registration N507RV, nosed over during an off-airport landing following a loss of engine power near Byron Airport, Byron, California. The private pilot and single passenger were not injured. The aircraft sustained substantial damage to the vertical stabilizer, right wing, and lower airframe structure.
The local flight departed Byron Airport around 1650 under visual meteorological conditions with no flight plan filed. According to the pilot, after an uneventful preflight and engine run-up including a magneto check, he flew to a practice area north of the airport to perform aerobatic maneuvers. After executing two rolls and leveling at 4,500 ft mean sea level, the engine began to sputter, and the Vertical Power VP-200 display indicated the ignition system had reverted to backup mode. The pilot cycled the magneto switch and fuel selector without improvement. While returning to the airport, at about 3,500 ft msl, the engine lost all power.
The pilot declared an emergency on the airport common traffic advisory frequency and performed a forced landing into an alfalfa field approximately 2 miles northeast of the airport. During the landing flare, he held full nose-up elevator to prevent the nosewheel from contacting the ground. The aircraft fishtailed on the main landing gear; when airspeed reached about 30 knots, the nose dropped, the nosewheel contacted the soil, and the aircraft immediately nosed over. Both occupants released their harnesses and repositioned themselves in the inverted cabin. The sliding canopy became impinged against the soil and could not be opened; the pilot kicked at its Plexiglas sides, creating a hole large enough to exit approximately 20 to 25 minutes after the accident. Emergency response personnel arrived about 10 minutes later.
Aircraft and Engine Information
The aircraft was equipped with a four-cylinder normally aspirated, fuel-injected experimental engine (Xtreem 360, model IO-360-B1BC3, serial number 6D081429) built by Eagle Engines using Superior Air Parts components. The engine was fitted with an FAA-certified Champion Aerospace LASAR electronic ignition system and a Whirlwind two-blade constant-speed composite propeller. The aircraft was completed in 2009 and first flown in March of that year; total time at the accident was 311.6 hours according to the tachometer.
The aircraft also carried an Advanced Flight Systems combination electronic flight instrument and engine monitor capable of storing parameters at 5-second intervals. Data from the accident flight indicated an increase in engine speed to about 1,800 RPM approximately 4 minutes after engine start, consistent with a magneto check, lasting about 30 seconds. About 11 minutes and 30 seconds after takeoff, at a GPS altitude of nearly 5,000 ft, manifold pressure dropped from 25 to 15 inches of mercury and fuel flow from 12 to 7 gallons per hour. Over the following 90 seconds, the aircraft descended; engine speed remained at 2,400 RPM while exhaust gas temperatures rose about 200°F and cylinder head temperatures dropped about 75°F. At 2,000 ft, engine speed dropped to 1,400 RPM as manifold pressure increased to 28 inHg. Exhaust gas and cylinder head temperatures then decreased until the recording ended 2 minutes later. Oil temperature and pressure remained stable.
Examination and Testing
Post-accident examination revealed no evidence of catastrophic engine failure. The crankshaft rotated smoothly by hand, all fuel lines were intact, and spark plugs exhibited normal wear. Ignition switch continuity was confirmed. Timing checks using a Champion Aerospace T-300 SyncroLASAR timing system showed the right magneto was correctly timed, but the left magneto's top dead center light remained illuminated and the BKR/PT light did not activate, indicating a failure per the maintenance manual.
Removal of the left magneto revealed its steel drive gear had become detached and was found loose inside the accessory case. The gear remained attached to the rotor shaft end, but the shaft had fractured at the main magneto bearing. Fracture surfaces were cup-shaped with uniform granular features and no beachmarks typical of fatigue. The engine's accessory drive gear teeth were intact; one tooth on the separated magneto gear had a 3-mm-long gouge.
Both magnetos and the LASAR control unit were examined at the Champion Aerospace facility in Liberty, South Carolina. The left magneto (Slick Model 4771) could not be dynamically tested due to the drive gear separation; internal components were intact and clean. The right magneto (Slick Model 4755) was tested on a bench: it sparked correctly in LASAR mode but produced intermittent sparks in backup mode and indicated an internal timing of 41 degrees instead of the nominal 25 degrees. Disassembly revealed the contact points were incorrectly adjusted; after correction, the magneto operated correctly in both modes. The LASAR controller passed all acceptance tests except for left and right coil current, which measured about 12 percent above nominal.
Previous Maintenance
According to the pilot, approximately 20 flight hours before the accident, he had experienced uneven engine operation in backup mode with high RPM drops (180–200 RPM) during magneto checks. After consulting Champion Aerospace, he sent the magnetos to a repair facility for a 500-hour inspection per the L-1503E overhaul manual. The repair shop replaced contact and cam assemblies in both magnetos and the coil in the right magneto. The pilot reinstalled the magnetos and adjusted timing using the T-300 tool; subsequent preflight checks showed normal RPM drops.