What happened
On June 9, 2020, an experimental, amateur-built Vans RV4, registration N173CW, was involved in a fatal accident near Safford, Arizona. The flight departed from Tucson International Airport (TUS) at approximately 08:10 MST, climbing to an altitude of about 9,800 ft MSL. After flying over mountain passes for approximately 25 minutes, the aircraft began a descent toward Safford Regional Airport (SAD).
ADS-B data shows that about 1.25 miles short of runway 30, the aircraft slowed to 110 kts. Shortly thereafter, the airplane entered a rapid descent of approximately 5,000 fpm over a 15-second period while accelerating to 150 kts. The aircraft struck the ground at an elevation of 3,090 ft MSL, approximately 500 ft north of the last recorded ADS-B position and 1/2 mile southwest of the runway 30 threshold. The impact caused substantial damage to the aircraft, and the pilot sustained 1 fatal injury.
The investigation
Due to pandemic restrictions, local law enforcement provided initial photographic documentation. Subsequent examinations of the airframe and engine were conducted by the NTSB, FAA, and Lyers Engines representatives. The investigation found that the aircraft's flaps were fully extended at the time of impact. While the electrical system for the flaps was too damaged to assess functionality, the actuator jackscrew was fully retracted, consistent with full deployment.
Investigators identified a 300-ft-long debris field. The engine remained attached to its mount, and there was no evidence of catastrophic internal engine failure or bird strike. However, the investigation noted that the rear control stick was missing its boot, leaving an opening in the floorboard. A position light socket, which had been previously removed from the aircraft, was discovered in the underfloor bay area of the aft control stick assembly. This socket had been wrapped in electrical tape and had cut conductor wires.
Findings
Flight testing conducted by Vans Aircraft using a similar RV-7 model determined that while flap deployment can cause a nose-down pitch tendency, the resulting control forces are manageable and can be overcome with aft stick pressure. The investigation concluded that the presence of the loose position light socket in the control stick assembly area presented a risk of interference with the flight controls.