A 707 crashed north of Seattle in 1959 during a pre-delivery test flight - apparently they were testing a new yaw damper and in the process performed such a radical maneuver that three of the four engines departed the aircraft. They were too heavy to make it back to an airport and set it down in Stillaguamish River, killing the four people in the flight deck (four others in the back survived)
https://aviation-safety.net/database...?id=19591019-0