Page:CAB Accident Report, United Airlines Flight 21.pdf/50

 Radio Equipment

The radio equipment was badly damaged and an inspection gave no satisfactory indication as to its condition prior to the crash. The aircraft was completely equipped with proper radio equipment and there is no reason to believe that it was not functioning properly. Two-way communication was maintained until less than one minute before the crash. In addition, the trip log bears a notation that the radio was operating "O.K."

STALL CHARACTERISTICS OF THE AIRPLANE

The maneuver which United 21 performed just prior to crashing was described by witnesses as an "exaggerated stall". In order to determine what might have caused the stall to develop, it is necessary to consider the flight characteristics of the airplane. In so doing we have available testimony of pilots at the hearing and reports of tests made of the DC-3.

The stall characteristics of the DC-3 with power off are considered to be quite satisfactory. When a stall occurs it develops at the center section before progressing to the wing tip and good lateral control is maintained almost to the stalling speed. An incipient stall is accompanied by vibration and tail buffeting which develops at a speed of about five miles per hour above the actual stalling speed. There is no marked tendency for the airplane to roll off in either direction, and it may be held in the stall without rolling unless the stall has been induced by pulling the nose up sharply. The recovery is quite readily made and may require between 100 and 500 feet, depending upon the severity of the stall.

Tests have shown that when a stall develops under the application of cruising power it does so rather abruptly and is accompanied by a violent