Investigation Summary
The accident aircraft, N9MB, was the fourth and final N-9M built, serving as a one-third scale flight test vehicle for the Northrop XB-35 bomber program. On the day of the accident, the pilot was performing a local test flight following the completion of the aircraft's annual inspection. Radar data showed the aircraft on an easterly heading but failed to capture altitude information. Witnesses reported the aircraft was at a low altitude when it performed a series of erratic maneuvers, including a pitch-up and a rapid roll to the right. During the descent, the engine RPM was heard to increase significantly. The aircraft impacted the ground in a near-vertical, high-speed attitude within the grounds of the California Rehabilitation Center. Investigators found the pilot's seatbelt unbuckled and the canopy separated from the main wreckage, suggesting an attempted but unsuccessful emergency egress. Although the N-9M design was historically known for a susceptibility to control reversal in steep spins, the NTSB could not confirm if this or a mechanical failure initiated the sequence due to the severity of the impact damage.
Final Conclusions
The NTSB concluded the investigation with a final report issued in January 2021. The probable cause was cited as the pilot's loss of control for undetermined reasons. The report noted that while all major structural components were accounted for, the fragmentation of the airframe and engines precluded functional testing of the flight control hydraulics or engine systems. Toxicological findings of ethanol and pseudoephedrine were determined to be non-contributing factors; the NTSB noted that the detected ethanol likely resulted from post-mortem microbial production rather than ingestion.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Pilot
David Vopat. Held an airline transport pilot certificate and multiple type ratings.
Systems & Failure Modes
Flight Controls
The N-9M used a radical all-wing design with elevons for pitch and roll control. The system included hydraulic components which could not be functionally tested post-crash.
Franklin XO-540-7 Engines
The N-9MB was powered by two 300hp Franklin engines in a pusher configuration. Witnesses reported hearing engine modulation and sputtering during the loss of control.
Interesting Facts
- 01The N-9MB was the last of four N-9M prototypes and the only one remaining in flying condition.
- 02The pilot was identified as David Vopat, a certified flight instructor with over 20,000 hours of total flight experience.
- 03The aircraft impacted the ground right wingtip first, creating a 16-foot long impact crater.
- 04Investigators found the pilot's seatbelt unbuckled, suggesting an attempt to bail out using his parachute.
- 05The wreckage was so severely fragmented that functional testing of the flight controls was impossible.
Location
ACCIDENT SITE · Coordinates taken from the wikidata coordinate.