A Comparison of Two Takeoff Flap Retraction Standard Operating Procedures

Takeoff 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 maximum thrust reduction from the takeoff thrust setting to the climb thrust setting. Timing of the flap retraction is critical to avoid over speed or under speed. Also, due to the vicinity of terrain and traffic, the vehicle performance and airspace must be carefully monitored all the 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 the “call out” by the Pilot Flying (PF) for each flap retraction. The other procedure delegates flap retraction to the Pilot Monitoring (PM). A formal analysis of the procedures using the HMI-Sequence Diagram 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 and dealing with interruptions. The implications and limitations of the formal analysis of procedures is discussed. Keywords—Human-Machine Interface; Standard Operating Procedures; flight deck operations; formal methods