Page:CAB Accident Report, United Airlines Flight 21.pdf/54

 ice accumulation described by these pilots was greater in amount and was in a more critical location than the ice which was found on United 21. It is reasonable to assume that this might be expected inasmuch as each of these aircraft was in the overcast for a period of approximately 25 minutes whereas United 21 was in the overcast for an estimated period of only 8 minutes.

In addition, Captain John L. Magden, a pilot for Transcontinental & Western Air, Inc., and Captain Charles A. Thompson, a United pilot, testified with respect to the flight characteristics of the DC-3. Captain Magden stated that on landing at Chicago at 3:52 on the afternoon of the crash with about ¼ of an inch of clear, smooth ice on his wings, the ship stalled on landing at a speed of approximately 80 miles per hour, more then 10 miles per hour above what he considered to be the normal stalling speed. Captain Magden also reported an experience wherein he used full throttle to maintain flying speed because of ice. Several similar cases have been reported by airline pilots.

A few days after the accident Captain Thompson made several tests on a DC-3 under icing conditions to determine the effect of ice on the speed at which the stall develops. These tests were made at night in a freezing mist, using a regular United DC-3 loaded to 22,900 pounds with the center of gravity at the 17 per cent position. United 21 is thought to have been loaded at the time of the crash to 22,690 pounds with a center of gravity position located between 18 and 24 per cent, depending upon the seating arrangement of the passengers. United 21 was equipped with the new type of de-icer boot having a flap extending over the attachment strip at the rear of the boot designed to eliminate the building-up of a ridge of ice along this