Page:CAB Accident Report, Continental Airlines Flight 12.pdf/11

- 11 - occurs when there is standing water on the runway surface, viscous hydroplaning which occurs when the runway surface is damp, and reverted rubber hydroplaning. (See footnote 8.)

Dynamic hydroplaning occurs when a tenth or more of an inch of water on the runway acts to lift the tire off the runway and the tire is supported by a water film. Viscous hydroplaning occurs due to the viscous properties of the fluid, water or slush. In this case a very thin film of fluid, a thousandth of an inch or so, cannot be penetrated by the tire, and the tire rolls on top of the film. This can occur at much lower Speeds than dynamic hydroplaning but requires a smooth or smooth acting surface. Reverted rubber hydroplaning requires a prolonged locked wheel skid, reverted rubber, and a wet runway surface. The witness theorized that reverted rubber acts as a Seal between the tire and the runway and delays water exit from the tire footprint area. The water a heats and is converted to steam and the steam supports the tire off the pavement. He believed that all three types of hydroplaning occurred.during the landing roll of Flight 12.

This witness prepared a calculation of the landing roll of the aircraft based on the crew's testimony, the flight recorder readout, and aircraft data provided by the aircraft manufacturer and the Board. His calculation shows that the aircraft had decelerated to 39 knots when it left the end of the runway. His calculations also indicated that only 11.2 percent of the stopping energy applied to the aircraft was induced by the wheel brakes in this accident. The total stopping energy available from the varied application of reverse thrust was 4.4 percent and the majority of the stopping energy, 84.4 percent, was a combination of aerodynamic drag and rolling resistance in this case. He performed another calculation based on the use of 100 percent reverse thrust to "0" velocity, with all other factors the same, which showed that the aircraft would have stopped after 5,560 feet of roll. However, he testified that this calculation neglected the loss of reverse thrust due to the cross ingestion of exhaust gases and that this loss would practically insure that the airplane could not have stopped on the runway.

As a result of the flight engineer's reported injury, during the final vertical impact, a special study was conducted of his seat. It was determined that the seat does not-have a metal bottom as the other crew seats have; but the cushion is held by plastic straps. These straps stretch in service and are within 1/4 inch of the heavy metal column on-which the seat is mounted. While no accurate estimate of the vertical loads applied to this aircraft could be made, it was noted that a test load of 8 feet/sec. imposed a peak load of 20 G over 40 milliseconds on a test dummy. This is the range of loading in which ejection seats operate and has been known to cause spinal injuries.

1.16 Water Accumulation

Testimony was taken during the deposition regarding the accumulation of water during periods of heavy rain. Tests in this respect indicate that.on 3 paved Surface with a transverse fall of 1 part in 150, a precipitation rate Of 3/4 inch per hour left 0.2 inch of Water standing on the pavement. In this connection the witness extrapolated the water accumulation-on the Kansas City runway, based on the reported_rate of rain fall, and estimated that 0.3-0.4 inch of water was standing on portions of the runway at the time Flight 12 landed.