The preliminary analysis discussed here is the result of an observational study. This methodology poses some limitations for identifying cause-effect relationships--mainly that the factors are not directly manipulated by the experimenter (Cook and Campbell, 1979). Bearing in mind this limitation, one may interpret the initial results presented here as suggesting the following:
First, within the possible mode space there are certain mode combinations that are frequently used. Pilots use several standard and preferred paths for mode transitions during the progress of the flight. Second, these mode transitions are influenced by the aircraft altitude and two environmental factors: type of ATC clearance, and the type of ATC facility (Approach Control, En Route Control, etc.) providing these clearances. We offer several possible explanations for this. (1) Altitude is a primary factor with respect to both short term (tactical) and long term (strategic) activity on the flight deck; and therefore, directly or indirectly it influences mode transitions; (2) ATC clearances prompt mode transitions. This comes as no surprise, since modes are a method for executing the tasks directed by ATC; (3) ATC facilities vary in the type and rate of clearances. For example, ATC controllers in an Approach Control facility issue mostly tactical clearances (e.g., maintain heading of 280 degrees, descend to 6000 feet) at a high frequency while demanding a quick response. In contrast, ATC controllers in En Route Control facility issue mostly strategic clearances (e.g., a complete route of flight between several waypoints). Evidence on the influence of both ATC Facility and clearance type on pilots' mode engagement was also found by Casner (in press).
Taken as a whole, these preliminary findings point to the important relationship between the modes structure of the automated system, and the task demands coming from the operational environment. The results of this relationship, or interaction, are the mode transitions in the system (see Figure 4).
Understanding both the automated system and the operating environment, as well as their interaction, appears valuable for designing new automatic flight control systems. This may be particularly important as future aircraft and the next-generation ATC system are likely to be very different from today's.
--A. Degani et al., "Mode Usage in Automated Cockpits: Some Initial Observations," Proceedings of the International Federation for Automatic Control (IFAC)