The Boeing 707 N7071 was operating on a customer guarantee and acceptance training flight prior to delivery of the plane to Braniff. The plane was being flown by a Braniff captain and a Boeing testpilot as instructor. Other Braniff and Boeing personnel were on board as crew members and observers. A series of Dutch Rolls were performed; one of the rolls was executed beyond the maximum bank restrictions. Control was lost, but the aircraft recovered. During the recovery however, the no. 1, 2 and 4 engines were torn off. An intense fire burned away portions of the jet control near the no. 2 engine attachment area. An emergency descent was carried out and the plane crash-landed along river. PROBABLE CAUSE: “The structural failure induced during an improper recovery attempt from a Dutch Roll which exceeded the angle-of-bank limits prescribed by the company.”