Page:CAB Accident Report, American Airlines Training Flight 514.pdf/7

- 7 - idle to full power could be as high as six seconds. The Boeing Airplane Company recommends that all thrust levers be retarded immediately in case of any out-of-control situation and thrust levers then be advanced on all engines together. The rolling maneuver could have been stopped rapidly by reducing power to engines Nos. 1 and 2, since the yawing forces and the high unequal rudder forces would have been eliminated. However, even had this procedure been followed it is questionable whether sufficient altitude remained to effect complete recovery.

In the flight configuration that had been established, the asymmetrical power condition would tend to create yaw to the right and would require the application of opposite controls, particularly left rudder, to compensate for the unbalanced thrust.

The rudder characteristics of the Boeing 707 are such that when yaw angles in excess of approximately 10 degrees are attained, the rudder effectiveness deteriorates quite rapidly with a resultant loss of directional control. This can produce a dangerous flight condition. In order to minimize the probability of large yaw angles during flight with both engines on one side inoperative, directional control must be maintained with the rudder. Excessive aileron or bank angles should not be used to maintain directional control. Yaw angles of approximately 10 degrees require nearly full aileron control to maintain heading when inadequate rudder is applied. There is also a noticeable stiffening of rudder pedal forces during the last two or three degrees of rudder deflection. Therefore, the pilot must be certain to depress the rudder pedal fully whenever a maneuver requires full rudder deflection. It is extremely important that the employment of rudder be positive and properly timed.

It is apparent that roll due to yaw resulted either from a lack of application of sufficient rudder, or an inadvertent release of left rudder. Since there is a noticeable stiffening of rudder pedal forces during the last two or three degrees of rudder deflection, it is possible that in this maneuver, where full rudder was needed to make the turn to final approach with Nos. 3 and 4 engines at idle thrust, full left rudder was not utilized. If this were the case, a yaw of as much as or more than 10 degrees could be brought about as the aircraft was banked to the left. Such a yaw would produce a violent roll to the right due to the aerodynamic response of the aircraft to yaw.

The student might have released the controls after assuming the instructor was taking over to initiate evasive action following his observance of a light aircraft low and to the right of the Boeing 707's flight path. Subsequent flight tests have revealed that the light aircraft could have been an alarming factor and a possible cause for evasive action on the part of the Boeing 707 crew. The instructor, sitting on the right side, could have indicated that evasive action should be taken and in the process of his taking control of the aircraft, the student relaxed rudder pressure before the instructor assumed control of the rudders. These circumstances pertaining to the presence of a light airplane are conceivable, however, certain points are difficult to resolve. First, it is believed that a prudent instructor would keep ahead of the maneuver, especially in jet transition training and particularly in the type maneuver being conducted, and prevent the development of a critically unsafe condition. Secondly, the testimony given by a Boeing test pilot attested that evasive maneuvers could be accomplished successfully even though the aircraft was in an asymmetrical power condition.