What happened
During a pre-delivery demonstration and acceptance flight, a Boeing Airplane Company test pilot was conducting instruction for an airline captain. The session involved performing various maneuvers, including the execution of Dutch Rolls. During one such maneuver, the aircraft reached a bank angle between 40 and 60 degrees, which surpassed the company's established safety limits for such demonstrations.
As the trainee attempted to recover from the roll, they applied full right aileron while the right-side bank was still increasing. The instructor pilot responded by applying immediate opposite aileron input. This corrective action caused the aircraft to swing past a vertical position and enter a violent left roll. Following several oscillations, the crew discovered that three of the four engines had detached from the Boeing 707 and the airframe was on fire.
The resulting fire severely compromised the control of the aircraft. While the crew attempted an emergency landing, they were forced to shut down the single remaining engine to maintain wing levelness. Consequently, the aircraft struck trees and crashed before reaching the intended runway. The accident resulted in four fatalities and four injuries.
Findings
The investigation concluded that the primary factor was the structural failure of the airframe caused by an improper recovery technique during a Dutch Roll maneuver that had exceeded prescribed bank angle limitations.