DEN93FA066
DEN93FA066

HISTORY OF FLIGHT

On June 5, 1993, at approximately 0745 mountain daylight time, N3005L, a Cessna 310J, was destroyed when it caught fire while parked on the ramp at the Jefferson County Airport, Broomfield, Colorado. One pilot received a minor injury when he jumped from the airplane; the other pilot escaped uninjured. Visual meteorological conditions prevailed at the time,and no flight plan had been filed for this planned instructional flight.

According to the pilot-in-command, the instructor-trainee had completed a preflight inspection of the airplane, and the two men were sitting in the cockpit discussing the lesson plan. No switches had been turned on. Fire and smoke immediately appeared and they jumped from the airplane.

WRECKAGE INFORMATION

Three "hot spots," or paint blisters, were noted on the exterior of the airplane: the left and right sides and top of the nose section, just forward of the windshield. At the latter location, the fire had burned through to the outside of the airplane. There was another burn-through hole in the center and on top of the glare shield. Both of these burn-through holes bore evidence of extreme heat and "blow torch" characteristics. The fire pattern was traced back into the nose wheel well where the cabin oxygen system supply bottle was mounted. The mounting collar and PUSH-PULL cable that connects to the system's ON-OFF handle were still connected. The cable was cut and the bottle was removed. Half of the regulator was burned away; the other half was still screwed into the neck of the bottle. The thermal relief valve had released all pressure. A sooty or carbonaceous appearing material was noted on the loop of the cable where it attached to the regulator.

TESTS AND RESEARCH

Maintenance records indicated the oxygen bottle was removed on May 20, 1993, for hydrostatic testing. On May 27, when the bottle was reinstalled in the airplane, it was discovered that the regulator leaked when pressure reached 1500 PSI (pounds per square inch). The low pressure relief valve was found leaking and a mechanic tapped the valve with the butt end of a screwdriver. The leak was said to have stopped and the oxygen bottle was then serviced to capacity (1600 PSI).

The airplane owner later checked the airplane's oxygen system and found the ON-OFF handle was stiff and the regulator was still leaking. According to the owner, a mechanic crawled into the nose wheel well, pulled on the cable, and was successful in closing the valve and stopping the leak. The owner said the mechanic then used an aerosol spray can to lubricate something in the nose wheel well but he did not know exactly what it was. The mechanic denied this but said he did lubricate the cockpit end of the regulator control. The regulator began leaking again when the system was activated. The system was turned off but was not depressurized. No entries were made in the maintenance records to reflect the regulator leakage or the difficulty in operating the control. On May 28, the owner flew the airplane to St. Louis, Missouri. When the airplane returned, it was parked on the ramp where it remained until the morning of the fire.

ADDITIONAL INFORMATION

The West Adams County Fire Department, which responded and assisted in extinguishing the fire, dispatched its arson squad to assist in the fire investigation. According to its report (see exhibits, attached), the cause of the fire was "friction of escaping oxygen igniting lubricant on cable." The report stated:

"It is believed the fire occurred as a result of a slow leak in the oxygen bottle valve assembly which finally ruptured and began to release oxygen under pressure onto the cable assembly which appears to have some form of lubricant applied to it. The escaping oxygen created an extremely large amount of friction and heat which sparked the lubricant and then ignited the oxygen creating a blow torch effect on the wall separating the cockpit and nose cone area where the oxygen bottle was located, breaching the wall, and igniting the dash board and cockpit area of the aircraft."

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