Say Again? How Complexity and Format of Air Traffic Control Instructions Affect Pilot Recall
Introduction
Until recently, controllers were required to communicate all numerical air traffic control (ATC) information in
sequential format, that is, digit by digit. For example, an altitude of 17,000 ft had to be transmitted as "Climb
to one seven thousand." According to the latest versions of the Air Traffic Control handbook (7110.65G), however,
controllers may restate altitude clearances in grouped format as "seventeen thousand" after giving them in sequential
format. Although controllers appear to generally agree that grouping numbers improves recall, there is no direct
scientific evidence to support this belief.
This study compared the recall of ATC information presented in either grouped or sequential format in a part-task
simulation. It also tested the effect of complexity of ATC clearances on recall, that is, how many pieces of information
a single transmission may contain without resulting in a readback error.
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