As they climbed to , the number-four engine stopped and the propeller began windmilling (rotating freely) in the airstream. Hitting the switch that would stop the propeller's spinning, Butchart found it slowed but then started spinning again, this time even faster than the others; if it spun too fast, it would break apart. Their aircraft needed to hold an airspeed of to launch its Skyrocket payload, and the B-29 could not land with the Skyrocket attached to its belly. Armstrong and Butchart brought the aircraft into a nose-down attitude to increase speed, then launched the Skyrocket. At the instant of launch, the number-four engine propeller disintegrated. Pieces of it damaged the number-three engine and hit the number-two engine. Butchart and Armstrong were forced to shut down the damaged number-three engine, along with the number-one engine, due to the torque it created. They made a slow, circling descent from using only the number-two engine, and landed safely.