Flight 81 · Beech 1900

The flight crew of a cargo airplane had previously loaded a cargo of carbon dioxide cylinders, and then flew to an intermediate airport for fuel. The cylinders had a screw type valve, and a threaded metal safety cap to protect the valve. During the takeoff run after refueling, the crew aborted the takeoff, and taxied back to the airport ramp after hearing a "hissing" sound from the cargo area. Once on the ramp, the captain shut off the engines, but the flight crew lost consciousness before they could exit the airplane. Since the crew filed an IFR flight plan that was not activated, air traffic control personnel contacted the freight office to inquire about the status of the airplane. A freight agent noticed the airplane sitting on the ramp. He opened the door of the airplane, and found the first officer unconscious, inside the door. The captain was unconscious at the controls. He pulled both crewmembers out of the airplane, and ran for help. The flight crew regained consciousness while lying on the ramp, and walked to the freight building. The flight crew were treated at a hospital and released the following day. The first officer reported that as the captain was taxiing back to the airport ramp, he felt the effects of the gas release, and he and the captain opened the cockpit windows. Once stopped, he got up to open the forward door, but collapsed at the door. An FAA inspector examined the airplane, and discovered that the cargo compartment had two tank racks containing five bottles each, standing vertically along each side of the airplane. Two of the cylinders in the left side rack did not have any safety caps installed. Three of the cylinders in the right side rack also did not have any safety caps installed. The caps were found on the floor of the airplane. The inspector found that the middle tank of the three in the right side rack, had a partially open valve. The open tank valve was about 1/2 turn open, and was positioned against the interior side-wall of the cargo compartment. The FAA inspector also indicated that nine carbon dioxide tanks were lying on the floor of the cargo area. They were braced by chocks, but were not strapped down. The crew oxygen masks were not utilized, and the crew oxygen supply tank was full. An FAA Hazardous Materials Division inspector reported that cylinders of carbon dioxide are considered hazardous material because they are pressurized in excess of 40 psi. The inspector noted that the shipper had a responsibility to properly identify and declare hazardous materials that they were shipping, the carrier had a responsibility to properly train airplane crewmembers to identify and accept hazardous materials, and the flight crew had a responsibility to properly secure hazardous materials during transport.

Verbatim NTSB analysis and probable cause from the NTSB dataset