appropriate. Provision of feedback about high level states of the system at any point in time is a design principle that should be followed for both approaches to automation. These and other parameters of adaptable automation should be examined with respect to operational concepts of air traffic management.
In theory, adaptive systems may be less vulnerable to some of the human performance problems associated with static automation (Hancock and Chignell, 1989; Parasuraman et al., 1990; Scerbo, 1996; Wickens, 1992; but see Billings and Woods, 1994). The research that has been done to date suggests that there may be both benefits and costs of adaptive automation. Benefits have been reported with respect to one human performance vulnerability, monitoring. For example, a task may be automated for long periods of time with no human intervention. Under such conditions of static automation, operator detection of automation malfunctions can be inefficient if the human operator is engaged in other manual tasks (Molloy and Parasuraman, 1996; Parasuraman et al., 1993). The problem does not go away, and may even be exacerbated, with highly reliable automation (Parasuraman, Mouloua, Molloy, and Hilburn, 1996).
Given automation-induced monitoring inefficiency, how might it be ameliorated? One possibility is adaptive task allocation, or reallocating a formerly automated task to the human operator. Given that an in-the-loop monitor performs better than one who is out of the loop (Parasuraman et al., 1993; Wickens and Kessel, 1979; but see Liu et al., 1993), this should enhance monitoring performance. But this is clearly not an allocation strategy that can be pursued generally for all automated tasks and at all times, for it would lead to excessive manual workload, thus defeating one of the purposes of automation. One potential solution is to allocate the automated task to the human operator for only a