Page:CAB Accident Report, Pan Am Flight 4.pdf/8

- 8 - There were three distinct fire patterns on the part of the wing which remained on the aircraft. (See Attachment No. 1.) One originated on the inboard gap cover area, followed the outboard nacelle upper surface support outboard to the trailing edge of the upper surface, and inboard to the inbound end of the outboard flap. The wing skin over all three fuel tank vent lines in this area was burned away or cracked for lenghts [sic] ranging from 44 inches over the forward vent line to 26 inches over the aft vent line. In this same area there were three holes, located in buckled skin, through the upper skin over the No. 4 main fuel tank.

The second fire pattern was in the area of the wing separation outboard of station 733. This fire consumed much of the portion of the aft spar remaining outboard of the production break and the centers of the access doors remaining with the attached lower skin. The fracture surfaces inboard of this area were extensively burned and metal sprayed while those on the separated panel had little heat damage and no soot deposits.

The third fire area was defined by heavy sooting and/or consumption of much of the outboard skin and ribs along the entire length of the nacelle strut trailing edge fairing. Finally, metal droplets were found on the right horizontal stabilizer and on the outboard three wing vortex generators in the aft row.

The outboard wing section that separated from the aircraft was extensively burnt and sooted. There was a ground fire where the wing section came to rest and the fire department reported using 250 gallons of water to extinguish it.

1.14 Survival Aspects

Prior to takeoff the stewardesses gave a passenger briefing and demonstration of the lifevests and oxygen masks and indicated the location of the emergency exits.

Following the loss of the engine and the outboard wing the passengers were briefed on ditching procedures and instructed to don their lifevests. After the decision was made to land at Travis AFB, the passengers were briefed by the cabin crew on preparation for an emergency landing including instructions on removal of shoes, sharp objects, etc., and the "braced position" to be assumed for the landing. Male passengers were placed at the emergency window exists and others chosen to assist with the evacuation slides.

The passengers assumed the braced position for the landing on instructions from the second officer who took charge of the cabin. The second officer and the cabin attendants opened the main entry doors and the galley service doors and, due to a lack of loading stairs, extended the evacuation slides. The captain stated that, to insure an orderly debarkation, he delayed the movement of the passengers until he was certain all stations were prepared. The debarkation was reported as orderly and took about four minutes from the time the aircraft stopped.

1.15 Tests and Research

Portions of the third stage turbine disk from the No. 4 engine were examined by the National Bureau of Standards and the Board's metallurgist. This examination revealed of circumferential fracture approximately two inches from the bottoms of the blade retention slots. This fracture occurred through a groove approximately