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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