In-Flight Engine Cowl Separation and Fuselage Damage During Cruise (N990CF)

Incident Overview and Immediate Response The aircraft was in cruise flight at 37,000 feet mean sea level when the crew heard a loud bang and the airplane shook. The crew immediately began to lose cabin pressurization. The engine instruments for the number two engine went dead, and the crew pulled the number two emergency 'T' handle. The crew donned their oxygen masks, began descending, and diverted to Denver. ## Post-Landing Examination Post-landing examination of the number two-engine nacelle revealed that the inboard and outboard main engine cowlings had separated from the aircraft. An 18 by 6 inch hole was found halfway up the fuselage, just aft of the left wing, at the pressure bulkhead. The left horizontal stabilator was also damaged. ## Engine and Bleed Air Findings Further examination of the engine revealed that the 4-inch-diameter high-pressure bleed air duct had separated from the high-pressure relief valve, and the clamp that connected them was missing. The clamp was never located. According to the operator, failure of the clamp would dump high-pressure bleed air into the nacelle, resulting in over-pressurization and separation of the cowlings. The wire bundle, which transmitted the number two-engine monitoring data to the cockpit, was found cut. There was no evidence of engine fire or fire in the nacelle cavity.