Overview
A Boeing Airplane Company test pilot was acting as an instructor-pilot on a demonstration and acceptance flight prior to the aircraft being delivered to the customer. The flight also included instruction for qualifying airline personnel on the aircraft. The instructor-pilot performed several maneuvers, including Dutch rolls, for a pilot-trainee—an airline captain on his first training flight before checkout on the Boeing 707.
Sequence of Events
The instructor-pilot initiated a Dutch roll maneuver that reached a roll-park angle of 40 to 60 degrees. This bank angle exceeded the company's established limit for demonstrating the maneuver. The pilot-trainee, who was tasked with recovering the aircraft, applied full right aileron while the right bank was still increasing.
Recovery Attempt and Structural Failure
The instructor-pilot immediately applied full opposite aileron. The aircraft stopped its right roll at a point well past a vertical bank and then rolled to the left more violently. Several gyrations followed. After control was regained, it was determined that three of the four engines had separated from the aircraft, and the aircraft was on fire.
Emergency Landing and Casualties
The fire rapidly reduced controllability. An emergency landing was attempted, but the aircraft struck trees and crashed short of the intended landing area because power on the remaining engine had to be shut down to keep the wings level. The aircraft was destroyed. Four crew members were killed, and four others were injured.
Probable Cause
The official investigation determined that the probable cause of the accident was the structural failures induced during an improper recovery attempt from a Dutch roll that exceeded the angle-of-bank limits prescribed by the company.