Analysis of Constant Time Delay Airborne Spacing between Aircraft of Mixed Types in Varying Wind Conditions

This study analysed the performance of constant time based airborne spacing under different operational conditions using fast time simulation. The effects of time based spacing criteria, mixed aircraft types and wind conditions on the ability of an aircraft to maintain a time spacing behind a descending lead aircraft were investigated. The spacing performance of a previously used approximate time delay spacing criterion based on current lead aircraft speed was compared with an exact time delay spacing criterion based on lead aircraft position history. The exact time delay spacing criterion resulted in smaller time delay spacing errors and smoother true airspeed behaviour. The exact time delay (60 s) criterion was then used to compare the spacing performance of a heavy aircraft following a light with a heavy aircraft following a heavy for different wind conditions. The results show that a heavy aircraft followed a light with approximately 40 % more maximum time spacing error than a heavy aircraft followed a heavy. Different effects for constant and turbulent winds were observed. Maximum spacing error increased slightly with constant wind speed but always remained within 10 s up to maximum constant wind speeds of 87 knots (at 30 feet altitude) and 235 knots (at 29,000 feet altitude). Turbulent winds severely degraded stability particularly in cross wind conditions.