Incident Overview
A cargo airplane, which had previously loaded a shipment of carbon dioxide cylinders, made an intermediate stop at an airport to refuel. The cylinders were equipped with screw-type valves and threaded metal safety caps to protect the valves. During the takeoff run after refueling, the flight crew heard a "hissing" sound emanating from the cargo area and aborted the takeoff. They subsequently taxied the airplane back to the airport ramp.
Loss of Consciousness and Rescue
After arriving on the ramp, the captain shut off the engines. However, before the crew could exit the airplane, both lost consciousness. Because the crew had filed an IFR flight plan that was not activated, air traffic control contacted the freight office to inquire about the airplane's status. A freight agent noticed the airplane sitting on the ramp and opened the door. Inside, he found the first officer unconscious near the door and the captain unconscious at the controls. The agent pulled both crewmembers out of the airplane and went for help. The flight crew regained consciousness while lying on the ramp and walked to the freight building. They were treated at a hospital and released the following day.
Crew and Cargo Details
The first officer reported that as the captain taxied back to the ramp, he felt the effects of the gas release. Both crewmembers opened the cockpit windows. Once stopped, the first officer stood up to open the forward door but collapsed at the door. The crew did not use their oxygen masks, and the crew oxygen supply tank was found full.
FAA Inspection Findings
An FAA inspector examined the airplane. The cargo compartment contained two tank racks, each holding five bottles, standing vertically along each side of the airplane. In the left side rack, two cylinders had no safety caps installed. In the right side rack, three cylinders also lacked safety caps; the caps were found on the floor. The inspector discovered that the middle tank of the three in the right side rack had a partially open valve—approximately 1/2 turn open—which was positioned against the interior side-wall of the cargo compartment. Additionally, nine carbon dioxide tanks were lying on the floor of the cargo area, braced by chocks but not strapped down.
Hazardous Material Considerations
An FAA Hazardous Materials Division inspector stated 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 being shipped, 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.