Page:CAB Accident Report, United Air Lines Flight 823.pdf/8

 Despite impact and fire damage, some information was obtained from the navigation and communications equipment. The two VHF radio transmitter selector switches were positioned on "No. 1 VHF Com." The No. 1 VOR navigation receiver was tuned to the Knoxville VORTAC. The No. 2 VOR receiver could not be identified. The omni bearing indicators read 066 and 148 degrees. The cockpit control head of the Air Traffic Control (ATC) radar beacon transponder was recovered positioned on Channel 11, Mode B; however, the Atlanta ARTCC radar had been receiving Channel 11, Mode A. Of the two automatic direction finding loop antennas, only one provided bearing information, 096 degrees. The distance measuring equipment (DME) as recovered was tuned to the Knoxville VORTAC with the mileage module locked at 47.5 miles. One altimeter was recovered, set at 29.82.

1.13

Both inflight and post impact fire occurred in this accident. The extent of the post impact fire as well as the extensive break-up hampered the investigation with respect to origin and progress of the fire. However, a comprehensive mock-up did permit some determinations in these regards.

Ground witnesses established by observations of smoke that there was an inflight fire. Burns and soot deposits on the free-fall victim and fire damage to bits of cabin material that fell away from the post impact fire area located inflight fire in the passenger cabin of the aircraft.

Examination of the wings, empennage, and powerplants did not reveal any evidence of inflight fire.

The fuselage beneath the cabin floor and rearward of the main spar (FS-414) contains the fuel burning Janitrol heater and is also the section through which the engine fuel system cross-feed line passes. The fuel line runs within a shroud which is vented to the outside. In the event of a double leak involving both the fuel line and shroud, fuel would not be released into the fuselage during pressurized flight. The Janitrol heater is not used in flight. There was no evidence of inflight fire in this area. This is the only portion of the fuselage that has engine fuel carrying lines.

Beneath the cabin floor, from FS-335 forward encompasses the cargo compartment and spaces containing some electrical equipment, including the inverters. Sufficient unburned cargo and airplane material was recovered from this area to eliminate the possibility of inflight fire in this portion of the fuselage. Likewise, the inverters did not reveal any signs of operational over-temperature. The investigation included a check of the cargo and stowed personal luggage for hazardous materials with all indications being that none were aboard.

The remaining portion of the fuselage beneath the cabin floor between FS-335 and FS-414 is known as the electrical bay. The generator and starter circuits are brought into the fuselage by means of feed-through studs through the fuselage skin at each side of this compartment. Through stud detail design provides specific safeguards to preclude conductor to ground faults. Circuits from these studs run to main distribution panels mounted on the forward face of the main spar. Also within this compartment are most of the electrical system control and switching relays utilized in the electrical supply system, the batteries, and a freon compressor. Hydraulic lines, some of which may be pressurized, depending on system demand,