A comparison of two takeoff and climb out flap retraction standard operating procedures

Takeoff and climb out flap retraction is a procedure that is conducted following takeoff to retract the flaps and slats from a takeoff configuration to a clean-up-and-away configuration. During this period the aircraft accelerates from the takeoff V2 speed to 250 knots and generally includes a thrust reduction from the takeoff thrust setting to the climb thrust setting. Timing of the flap retraction is critical to avoid overspeed or underspeed. Also, due to the vicinity of terrain and traffic, the aircraft performance and airspace must be carefully monitored while staying responsive to Air Traffic Control voice communication. As a result the design and certification of these procedures must resolve multiple conflicting objectives. This paper describes a formal analysis of alternate takeoff flap retraction procedures for the BAE 146 (Avro) aircraft. One procedure requires a “callout” by the Pilot Flying (PF) for each stage of flap retraction. The other procedure delegates flap retraction to the Pilot Monitoring (PM). A formal analysis of the procedures using the Human Machine Interaction Sequence Diagram (HMI-SD) method yielded equal utility. Overall, the Callout procedure is more robust to interruption and provides a better shared mental model between the crew members. However, the Delegate procedure can be completed on average 4.5 seconds faster providing more time for monitoring or performing other tasks. The implications and limitations of the formal procedure analysis is discussed.