328 Part 2 ½ Regions of Computer Space Section 3 ½ Concurrency: Single-Processor System

LIE, FAST TBAFFIC SEVEN O'CLOCK, 4 MILES, ALTITUDE 123 HUNDRED, NORTHEAST BOUND."

Top level flow charts for four of the associative programs, used in the demonstration are shown in Figs. 11, 12, 13, and 14. A detailed report is in preparation describing all of the ATC programs used in this demonstration, but some comments on the four flow charts shown may be of interest.

Live target tracking (Fig. 11) is performed in two dimensions (mode C altitude data was not available) using both radar and beacon target reports to track all aircraft. Incoming reports are correlated against the entire track file using five correlation box sizes, three of which vary in size with range. Any incoming report which does not correlate with an existing track is used to automatically initiate a new tentative track. An aircraft track must correlate on two successive scans and have a velocity exceeding 21 knots to qualify as an established track and must correlate on three successive scans to achieve a track firmness level high enough to be displayed to a controller as a live target. There are provisions for 15 levels of track firmness including 7 "coast" levels.

If a report correlates with more than one track, special processing (second pass resolve) resolves the ambiguity. Correlated new reports in all tracks are used for position and velocity smoothing once per scan via an alpha-beta tracking filter where for each track one of nine sets of alpha-beta values is selected as a function of track history and the correlation box size required for the latest report correlation. If both beacon and radar reports correlate with a track, the radar report is used for position updating. Smoothed velocity and position values are used to predict the position of the aircraft for the next scan of the radar and for the look-ahead period involved in conflict prediction.

Track simulation processing (Fig. 12) produces 256 tracks in three dimensions with up to four programmable legs for each track. Each leg can be of 0 to 5 minute duration and have a turn rate, acceleration, or altitude rate change. A leg change can be