Soon after the profile descent experiments were completed in 1979, Langley researchers began work on another concept aimed at improving the efficiency of ATC system operations by giving pilots better navigation information and capabilities in the cockpit. The idea was Cockpit Displayed Traffic Information (CDTI), and the researchers in the TCV/ATOPS program were interested in it because they saw it as "an important step in the direction of 'electronic VFR' (visual flight rules)." If pilots could "see" the other traffic in the area, it might allow reduced separation between aircraft, which would increase the efficiency and capacity of terminal operations. [Ref 7-12]

The idea of giving pilots better information about potential conflicting traffic had been around since the mid1940s, when researchers suggested that the new television and radar technologies might be combined to create a cockpit traffic display. [Ref 7-13] That idea never materialized, but in the early 1970s the Massachusetts Institute of Technology (MIT) received FAA sponsorship to conduct preliminary simulation studies of a more advanced cockpit display of traffic information. The MIT research indicated that the basic concept, at least, was well accepted by pilots. [Ref 7-14] Researchers in NASA's TCV/ATOPS program built on the MIT studies for a series of flight experiments in 1979 that tested both the basic CDTI concept and potential symbology for such a display, using the TSRV 737.

The CDTI flight tests, conducted in the fall of 1979, consisted of a total of 29 curved, decelerating approaches into the NASA Wallops Island Flight Facility in Virginia. The research pilots had to execute the approaches while they monitored the traffic situation and reacted to potential conflicts. The traffic displays were created by integrating traffic information into the electronic horizontal situation indicators (EHSI), or map displays, in the aft research cockpit. Since the focus of the NASA experiments was on the pilot's interface with a traffic display, the research flights used a prerecorded data tape of simulated traffic to create the images on the cockpit display. The tapes presented a realistic scenario of numerous airplanes following different flightpaths into the Wallops Island airport, however. The tapes could also provide the research pilots with scenarios in which the other pilots made mistakes in addition to normal, errorfree situations.

The format tested in the experiments was a "courseup" display, with twothirds of the viewing area in front of the symbol representing the pilot's own airplane. The position of the 737 was updated almost continuously, while the other simulated traffic was updated every four seconds to replicate the speed with which an ATC radar could complete a sweep and update a display. The pilots could choose six different scales for the display, ranging from one to 32 miles, and could set the display to show or suppress data blocks with more detailed information about each airplane symbol on the screen.

The research flights also tested both "coded" and "uncoded" formats for the traffic symbology on the display. Both formats showed the past and current position of each aircraft and a trend vector indicating where it was headed, but the coded symbology also told pilots whether the traffic was above, at or below their own altitude, whether or not it was under ATC control, and if it had CDTI capability.

The results of the flight tests indicated that the display improved pilots' situation awareness and made them willing to use closer spacing with other aircraft during approaches. The pilots liked the coded symbology, although they indicated that they did not need to know whether other aircraft were CDTI equipped or under ATC control. There were some problems with use of the display, however. The EHSI could get extremely cluttered, especially if the data blocks on each airplane were displayed. The researchers also found that pilots had a tendency to fixate on the display, which could cause problems in an operational flight environment, where pilots needed to maintain an effective scan of the instrument panel and the airspace outside the aircraft.

In addition, the tests showed that the raw display data was not really adequate for use in approach sequencing. It was difficult to detect if an airplane ahead was slowing down until so much of the gap had closed that the pilot following the CDTI had to reduce speed sharply to maintain adequate spacing. The researchers also saw that trying to maintain the same spacing throughout an approach did not work, because all the airplanes stretched out along the approach path would have to slow down at the same time and to the same speed as the one closest to the airport to maintain the same spacing. That meant that airplanes would be slowing down to final approach speeds many miles from the airport. [Ref 7-15]

Langley engineers conducted some followon simulator studies to research enhanced display formats that would allow a CDTI to be used for more efficient sequencing. NASA managers finally decided, however, that concepts such as 4D navigation could accomplish the same end as the CDTI technology with less difficulty. As a result, the CDTI technology was not pursued. The Traffic Alert Collision Avoidance System (TCAS) cockpit display the FAA later mandated for airliners did incorporate data on the location of potentially conflicting traffic, but the purpose of the information was for collision avoidance only, not for approach sequencing. [Ref 7-16]