History of Flight
On June 8, 2023, about 1124 Pacific daylight time, an experimental amateur-built Steen Skybolt, registration N202GM, was substantially damaged when it crashed near Rio Vista, California. The two pilots were fatally injured. The airplane was operating as a personal flight under Title 14 Code of Federal Regulations Part 91.
The front-seat pilot requested the aft-seat pilot to pick him up at Sacramento Mather Airport (MHR). The aft-seat pilot departed Concord, California, where the airplane was based, at about 1000. The front-seat pilot had dropped off another airplane earlier at MHR and needed to return to Concord.
Recorded radar data from the Federal Aviation Administration (FAA) showed a primary target starting near the departure point at 1059:09 and ending near the accident site at 1124:20. The flight track indicated a southwesterly direction. At 1115:30, the airplane made a 360° turn or maneuvering. At 1116:15, it continued south along the Sacramento River Deep Water Ship Channel. The returns became sparse and passed over Rio Vista Municipal Airport (O88), consistent with entering the downwind leg of the traffic pattern for runway 25 and then a left base leg. The track then showed a left hook shape consistent with a spiral.
A witness, a commercial pilot, reported hearing a transmission on the common traffic advisory frequency stating "experimental biplane, engine out." He observed the airplane flying from the north on a southerly heading over the airport at midfield. It turned onto a left downwind for runway 25 at an estimated altitude of about 1,000 ft agl. The airplane then banked left, followed by a loss of control, and within 10 seconds impacted the ground. The witness stated the engine sounded normal and added that the pilot could have said "simulated engine-out."
Another witness observed the airplane at a normal pattern altitude with the tail lower than usual. A witness at a nearby golf course saw the airplane enter a left bank about 750 to 1,000 ft agl, making several spirals before disappearing.
Aircraft Information
The accident airplane was a two-seat biplane with tricycle landing gear and dual controls, flyable from both seats. The pilots purchased it from the builder on November 2, 2022. Maintenance records from the prior owner were in the pilots' hangar; no records existed after purchase. The last annual inspection was completed on March 13, 2022, at tachometer time 511.2 hours. A pre-buy inspection was performed on June 28, 2022, at 515.4 hours. The airplane had accrued 543.9 hours at the time of the accident.
The build manuals specified a trim tab system with a McKenzie Vernier control, which was not installed on the accident airplane. Photographs of the installed trim system were shared with the builder, who confirmed it did not match his original configuration. The timing and origin of the modification could not be determined because logbooks were maintained only up to the sale.
A 40-second video from the pilot's iPad, recorded on January 18, 2023, showed a pilot manipulating the right trim tab up and down, remarking "see how much that moves." He then inspected the left trim tab, noting it was "stiff." He stated his belief that this was "what the problem was," describing how it "just started oscillating … throwing the elevator up and down." He concluded by stating he had found the issue and planned to fix it.
Meteorological Information
Local weather stations reported an average wind from about 255° at 10 knots, gusting to 15 knots.
Wreckage and Impact Information
The accident site was about 2,615 ft from the approach end of runway 25. Wreckage was distributed over about 45 ft on a true heading of 350°. The nose pointed on a median heading of about 20°. Initial debris included paint chips and an air scoop from the left fuselage; the furthest pieces were large splinters of wood from the two-bladed propeller.
The fuselage came to rest upright with lower wings attached at the roots. Upper wings remained attached but partially collapsed onto lower wings. Both lower wings sustained crush damage. Aileron control continuity was established. The empennage, vertical stabilizer, and rudder remained largely intact. Horizontal stabilizers were severely deformed. Elevator movement was restricted due to forward structure deformation. Rudder and elevator cables were continuous. The left trim tab remained attached; the right trim tab sheared off the piano hinge but remained connected to bellcranks. Neither trim tab moved freely. The cockpit trim control was in the neutral position; moving to nose-down shifted the surface upward, but the control could not move toward nose-up due to a binding sleeve.
Engine examination revealed multiple crankcase fractures, broken oil sump and intake manifold. Spark plug electrodes were consistent with normal operation but worn. Valve and gear train continuity was established; compression was detected in all cylinders. Combustion chambers showed light scratches and corrosion. No evidence of foreign object ingestion or detonation. The No. 3 exhaust valve showed high-temperature coloration. Pistons and rings were intact; skirts had scuffs/grooves. Cam lobes and lifter faces showed wear, with severe spalling on intake lifters. Both magnetos produced spark. No evidence of pre-mishap mechanical malfunctions was found.
Fuel consistent with 100LL was found throughout the system. Corrosion was present in the fuel servo. The oil filter and suction screen contained metal particles.
Medical and Pathological Information
Autopsies performed by the Solano Coroner's Office determined the cause of death as blunt force injuries.