chapter treats those aspects that deal primarily with interactions between humans and machines. These include the content and format of information that allows crew members to interact with each other and with the on-board automation, ATM personnel, and ATM automation; the transfer of information between crews and the ATM system; and information required within the ATM system.

There are two overriding, interwoven themes in this treatment. Expressed as key challenges, they are: (1) the improvement of overall ATM performance, and the enhancement of safety.

That the first challenge exists is obvious to even the most naive user of the existing ATM. The technical answers to performance and capacity improvements are the introduction of advanced new aircraft, equipment, and facilities into the transportation system.

The second challenge may not be so obvious, because the existing ATM is one of the safest ways ever developed for point-to-point travel. The introduction of advanced avionics, glass cockpits, new training procedures, and more reliable systems and subsystems in aircraft since the beginning of the wide-body jet era has probably played a part in establishing the current downward trend of total accidents in the United States. There are insufficient statistical accident data since the introduction of the newest transport aircraft (MD-11, 757, 767, 747-400, A320) to fully evaluate the safety improvements achieved with application of advanced technology and the existing human factors guidelines. It is clear that the traveling public will insist on maintaining a high safety record (as measured by absolute number of accidents, not rate