Page:CAB Accident Report, United Air Lines Flight 823.pdf/10

 recovered coated on the inside with soot and a white deposit which was similar to the white smoke given off when the vinyl cover on the left forward bulkhead is burned. The plastic window material had flow marks on it which indicated that it had been heated to approximately 626°F., while in an upright position. There was also evidence of pre-impact fire in the carry-on baggage rack and other areas in the forward cabin.

The firefighting equipment aboard the aircraft was examined to see if it had been used. Fire extinguishing systems are provided for the engines, underfloor cargo compartments, the Janitrol heater, and the cockpit and cabin. Three of the four engine bottle discharge heads were recovered but none showed signs of having been discharged by electrical means. The forward cargo compartment CO2 extinguisher had been fired electrically. No positive determination could be made as to whether the Janitrol heater compartment CO2 extinguishers had been fired. One of the two cabin CO2 fire extinguishers had been discharged and a cabin water extinguisher had been prepared for discharge; however, it had not been expended.

A flight crew walk-around oxygen bottle was recovered with the control valve open. The rubber diaphragm in the regulator had been discolored by smoke. One passenger oxygen bottle was found with the shutoff valve "open." a portion of one of the three installed flight crew full-face smoke masks was recovered but there was no evidence of its having been in use.

All three supercharger spill valve actuators were found with their actuating rods in the "supercharge spill" position. This setting would dump supercharger air overboard rather than using it to pressurize the cabin. The cabin pressure control located in the cockpit was set at the "sea level" selection and the cabin outflow valves were found in the manually depressurized position. The unpressurized flight valve electrical actuator was found in the "depressurized" position.

The interior locking mechanisms for the No. 4 and No. 9 windows on the left side were found in the unlocked position, and the captain's direct vision (DV) window was found unlocked and partially open. The copilot's DV window track and frame with attached cockpit liner showed evidence of heating and sooting. Adjacent portions of the cockpit liner that had been covered before breakup were clean. The window position at impact could not be determined. There was no evidence of an inflight fire originating in the cockpit portion of the fuselage.

The engines, underfloor cargo compartments, and the Janitrol heater are equipped with fire detection systems. The captain of the previous flight in this aircraft testified that he detected no problems with the fire warning systems when he tested them.

There is no smoke detection system other than the crew sense of smell or observation of smoke in the aircraft.

In normal operation cabin air is drawn down under the cabin floor and circulated back into the cabin by the recirculating fan through ventilators in the cockpit and cabin. Any smoke generated under the cabin floor would be transferred to the cabin and cockpit within seconds where it would be seen or smelled by the crew and passengers.