What happened
The aircraft was in cruise flight at 37,000 feet MSL when the crew heard a loud bang accompanied by significant airframe vibration. Following this event, the aircraft began to lose cabin pressurization. The engine instruments for the number two engine ceased functioning, prompting the crew to pull the number two emergency 'T' handle.
The crew donned oxygen masks and initiated a descent, diverting the flight to Denver. There were no injuries reported during the event.
The investigation
Post-landing inspections of the number two engine nacelle revealed that both the inboard and outboard main engine cowlings had separated from the aircraft. Investigators discovered an 18x6 inch hole in the fuselage at the pressure bulkhead, located just aft of the left wing. The left horizontal stabilator also sustained damage.
Detailed examination of the engine identified that a 4-inch-diameter high-pressure bleed air duct had separated from the high-pressure relief valve. The clamp intended to connect these components was missing and was not recovered during the investigation. Additionally, the wire bundle responsible for transmitting monitoring data from the number two engine to the cockpit was found to be cut. There was no evidence of an engine fire or a fire within the nacelle cavity.