Page:CAB Accident Report, Pan American World Airways Flight 212.pdf/9

- 9 - maintained as the aircraft proceeded down the runway, braking efficiency would have been limited by the effectiveness of the right MLG tires. The new ribbed tires on the left MLG probably accounted for the swerve to the left near the end of the run- way as these tires would brake more effectively than the right tires as the aircraft slowed.

Although the captain stated that he extended the speed brake (spellers) after touchdown, and in all probability believed that he did, the physical evidence showed that the spoilers were retracted at the time of impact with the water.

The fog bank involved extended at least to the approach end of runway 43 as shown by the RUB on runway 31L of 2,000 feet at 2254 and 2,600 feet on runway 4R at 2314. Reduction to these distances could only have occurred as a result of the fog. The extended centerline of the approach end of runway 31L is in proximity and crosses the approach end of runway 4R.

The captain stated " . . As we crossed the threshold I pushed the airplane down. . . " An analysis of the flight recorder readout shows this pushover oc- curred at an altitude of 400 feet and 12 seconds prior to touchdown. Using the average airspeed from.threshold to touchdown of 169 knots and adding a 5 knot tall- wind, the aircraft was making a ground speed of 174 knots for the 12 seconds prior to touchdown. At this Speed, and for this length of time, computations show that this aircraft would have touched down about 3,516 feet from the threshold, and would have left the surface of the runway at an indicated airspeed of approximately 82 knots. An increase in the magnitude of "G" trace deflections occurred 23 sec— onds after touchdown when the trace went from —.O25"G's" to + 2.52 G's."

At the average groundspeed of 132 knots (127 knots IAS plus 5 knot tailwind) for the 23 seconds following touchdown, FAA 212 would have traveled 5,120 feet on the runway. This dlstance subtracted from the length.of the runway shows that the touchdown paint was 3,280 feet from the approach end of runway 4R. From a touch— down ground speed of 165 knots (160 knots IAS plus 5 knot tailwind), the aircraft decelerated to 142 knots groundspeed during the next 10 seconds at an average speed of 151 knots at this average speed for 10 seconds, FAA 212 would have traveled 2:543 feet This distance added to the lesser of the computed touchdown points {3,280 feet) and subtracted from the length of runway 4R (8,400 feet) shows that when PAA 212 reached a groundspeed of 142 knots, there was only 2,577 feet of re- maining runway.

Boeing test data indicate that under conditions of wet runway at sea level zero wand, 196,000 pounds gross weight, anti-skld brakes on, attainment of maximum reverse thrust within 10 seconds after touchdown, spellers retracted, smooth tires, and a touchdown speed of 142.2 knots IAS, 4,350 feet of runway 15 required to stop the aircraft.

Examination of these data further shows that the elemination of any of the ad- verse factors related above would not have prevented the aircraft from overrunning the runway.