On April 27, 2000, at 2130 mountain daylight time, a Douglas DC-8-62F, N990CF, was substantially damaged when the number two engine cowling departed the airplane near Denver, Colorado. The airline transport captain and first officer, the commercial pilot flight engineer, and two passengers were not injured. The airplane was owned by Fleet National Bank of Hartford, Connecticut, and was being operated by Emery Worldwide Airlines, Vandalia, Ohio, under Title 14 CFR Part 121. Visual meteorological conditions prevailed for the night cross-country flight, which originated from Seattle, Washington, 2 hours 48 minutes before the accident. An IFR flight plan had been filed for the cargo flight that was en route to Dayton, Ohio. The captain said that they were in cruise flight at 37,000 feet mean sea level (msl). He said that they heard a loud bang and the airplane shook, and they immediately began to lose cabin pressurization. The engine instruments went dead on number two- engine, and they pulled the number two emergency "T" handle. He said that they donned their oxygen masks, began descending, and diverted to Denver. Their landing was uneventful. Postlanding examination, by the NTSB Investigator-In-Charge and an FAA Inspector, of the number two-engine nacelle revealed that the inboard and outboard main engine cowlings had separated from the aircraft. An 18x6 inch hole was found half way up the fuselage (pressure bulkhead), just aft of the left wing; the left horizontal stabilator was also damaged. 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 connecting clamp was missing. The clamp was never located. 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. According to the operator: "when the clamp assembly failed, high pressure bleed air from the 4 inch diameter duct dumped into the area inside of the engine cowlings. The sudden over-pressurization probably expanded the main engine cowlings into the air stream, leading to the loss of the cowlings. The amount of airflow from the high pressurization bleed air duct far exceeds the air discharge capacities of the cowling blowout panels."