Development of the enhanced bank angle warning

To reduce the risk of loss of control in-flight due to loss of attitude awareness, a new roll attitude alert was developed (Enhanced Bank Angle Warning). This alert consists of a moving red arrow on the primary flight display with a voice aural indicating the correct recovery action. The alert has two intended functions: (1) to increase the timeliness and likelihood of correct control input by the pilot flying, and, (2) to increase the timeliness and likelihood of intervention by the pilot monitoring (if the pilot flying fails to take appropriate actions). In the development of this alert, data on loss of control accidents and incidents were reviewed and various flight deck design elements were evaluated during prototyping for effectiveness in communicating aircraft state and recovery actions. Design elements studied included symbol shape, symbol motion, color, and the presence and content of voice aurals. Following prototyping, the ultimate design was evaluated in a pilot-in-the-loop simulation study with 19 airline pilots, including 5 non-native-English speakers. The two intended functions of the alert were tested in two scenarios: one intended to assess behavior of the pilot monitoring during an unexpected overbank condition and the other to assess behavior of the pilot flying in response to unusual attitude recovery scenarios. The results with respect to behavior of the pilot monitoring trended in a positive direction, but were not statistically significant. The results with respect to behavior of the pilot flying provide strong support for inclusion of the alert to improve pilot flying response to unusual roll attitudes. This paper reviews the prototyping phase, pilot-in-the-loop simulation results, and the challenges that were eventually overcome to implement the Enhanced Bank Angle Warning in Boeing's 737-MAX airplanes.