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inch. Normal contact patterns were evident in the inner center tang of the vanes. Several vanes were buckled and missing the inner platform. The fourth stage inner seal ring assembly was severely torn and twisted. normal vane patterns were evident on the rail section. The separated inner sealing ring was torn apart and severely rubbed. The fourth stage nuzzle guide vanes were damaged slightly on both the leading and trailing edges, most of the outer forward feet were broken, and several vanes were broken through the airfoil. There were varied temperature patterns visible on the guide vanes but no evidence of overtemperature. The lock rings for the nozzle guide vanes were recovered, severely distorted, as well as the outer seals which were also severely rubbed and distorted.
The turbine housing assembly was circumferentially gouged around the inner surface and the turbine exhaust case was collapsed in the horizontal plane and the interior of the case was severely scored and peened. The upper rear half of the turbine nozzle case was split open from the plane of the third stage turbine disk aft to the rear flange, and forward to the first stage turbine rotor.
1.13 Fire
There was evidence of fire on the separated wing section, the wing around the point of separation, and on the No. 4 engine. Fire was observed by ground witnesses, passengers and crewmembers, and photographed, in color, from the ground and by a passenger.
The flight crew was alerted to the fire when an intermittent fire warning was observed while they were going through the engine shutdown procedure following the failure of the No. 4 engine. The first officer then actuated the fire selector lever for the No. 4 engine and discharged both fire extinguisher bottles to the engine. The fire was observed to go out and did not recur although fluid was observed streaming from the right wing for the duration of the flight. Fuel was still streaming from the right wing, after landing, from the No. 4 tank area until the fire department plugged the hole in the bottom of the tank. The area around the fuel spill and the wing stub were formed as a preventive measure while the passengers were debarking from the aircraft.
Examinations of the fire extinguisher bottles in the right wing revealed that they were both empty and the discharge indicating disk was missing while the thermal discharge indicating disks were intact. The fire extinguisher line which runs along the forward face of the right front spar was severely chafed and worn through at about front spar station 653. The chafed area was on the bottom of the line where it contacts the front spar bottom cap, and was 6-1/2 inches ling and 5/16 inche wide at its widest point. A hole in the chafed area was 1 inch long and 1/8 inch wide. Aside from this chafed area the line was intact to a point 45 inches beyond the No. 4 pylon firewall where it separated from the engine plumbing. The No. 4 engine fire detector wiring was in the No. 4 pylon wire bundle and was charred in the upper pylon area, aft of the pylon firewall. The extremity of the wire was stripped of insulation and exposed to the airstream.
Fire damage to the No. 4 engine consisted of sooting of the accessory drive gear and a heat pattern in the left side cowl panel beginning 12 inches from the top of the cowl, at the leading edge, extending diagonally down and aft to a point 8 inches above the surge bleed door. This beat pattern was about 12 inches wide and consisted of molten metal on the side of the cowl and soot on the outside.
