Page:CAB Accident Report, United Airlines Flight 21.pdf/55

 strip. The ship tested was not equipped with this new type de-icer and the effect of ice may be greater than a corresponding accumulation on United 21. Captain Thompson accumulated a clear glaze ice of approximately ¼ inch in thickness, extending back 2-½ inches on top and bottom of the center line of the leading edge of the de-icer boot, together with a mass of rough ice extending from a point behind the smooth ice over the cap strip and running back onto the wing proper for a distance of about 6 inches. In Captain Thompson's opinion, this icing condition was roughly similar to that on United 21 except for the rough ice over the cap strip and back on the wing proper. He testified that with wheels down, three-quarter flap position, 17 inches of the manifold pressure and a descent of 400 feet per minute, the ship reached the point which he considered to be just above the stall point at an indicated air speed of 70 miles per hour. He reported that at 75 miles per hour the aileron control was still present. The ship stalled just above the ground on landing at an indicated air speed of 70 miles an hour, only 6 miles above the normal stalling speed of the same airplane under similar conditions without ice.

Captain Thompson made two other tests the same evening and photographs of the ice accumulated on these occasions were introduced into the record. On the second trip he accumulated ice of from ⅝ of an inch to one inch in thickness, very rough in character, extending over the leading edge of the wing. With the same setting as the first test, the ship gave indications of being near the point of stall at 71 miles per hour with aileron control still effective at 75 miles per hour. Captain Thompson stated that the only indication he had of the approaching stall was the sluggishness