Page:CAB Accident Report, Pan Am Flight 102.pdf/6



Results of the investigation indicate that the failure of the truck beam was due to a crack produced by impact loads on its top surface. The initial crack was propagated to complete fracture by additional impact and normal service loads. Some hydrogen embrittlement and an unusually large number of nonmetallic inclusions in the area where the fracture started may have contributed to the failure by decreasing the ductility of the steel.

As a result of a study of snubber failures, the manufacturer has prepared several changes which it is anticipated will eliminate further difficulty. The size of the orifices in the hydraulic piston of the snubber assembly are to be reduced to increase its load rate, and the pressure relief setting is to be increased from 8,000 p.s.i. to 12,500 p.s.i. These modifications will increase the effectiveness of the damping action of the snubber assembly. The automatic wheel braking valve setting is to be reduced from 450 p.s.i. to approximately 175 p.s.i. This should decrease the tendency of unequal braking causing the oscillation of the truck beam. In addition, the pressure in the leveling cylinder assembly is to be increased from 925 p.s.i. to 1,500 p.s.i.

These changes should prevent excessive oscillation of the truck beam caused by either unequal braking during retraction or by displacement of the truck during taxi or takeoff roll.

The Board concludes that the agreements between the Port Authority and New York Fire and Police Departments, which have been in existence for a number of years, are sound. Many emergencies have been covered in the past following the practices established in these agreements. While improvements, alterations, and modernization of the procedures are indicated from time to time, it is believed the policy of mutual assistance can and will continue to operate successfully. Subsequent to this accident, representatives of the National Association of Broadcasters have advised that when radio and television coverage of emergency news is being broadcast, a specific request will be made to listeners "to refrain from doing anything that would hamper the efforts of the authorities whose responsibility it is to cope with the emergency."

The Board realized that an aircraft emergency is news and that news reporting media constantly monitor aircraft radio frequencies. It is not to be inferred that this practice is in any way improper. It is a fact, however, that the public broadcasts in this case attracted large crowds of persons to the scene. The resulting traffic completely choked the access highway to the airport boundaries. This could give rise to a serious problem affecting air safety and one which will be given further study by the Board.

The Board determines that the probable cause of this accident was the failure of the forward truck beam of the left landing gear.

BY THE CIVIL AERONAUTICS BOARD: