What happened
While operating in cruise flight at flight level 310, approximately 20 miles west of Denver, Colorado, an all-cargo 14 CFR Part 121 aircraft encountered severe clear air turbulence. The encounter resulted in significant oscillations in both roll and pitch, along with major fluctuations in airspeed.
During the period of departure from controlled flight, the aircraft suffered severe structural damage. The number one engine and 19 feet of the left wing's leading edge separated from the airframe. Additionally, the pylon for the number four engine cracked and sustained substantial structural damage. Prior to this event, the flight had been experiencing light to occasionally moderate chop, and the forecast had indicated moderate to severe turbulence.
The crew performed a precautionary descent following the structural failures. The aircraft subsequently landed at Stapleton International Airport in Denver, Colorado.