A Linear Altitude Rule for Safer and More Efficient Enroute Air Traffic

Abstract

Current regulations designate cruising altitudes in discrete steps of 1000 ft (or 2000 ft above FL290, but those will eventually be reduced to 1000 ft also). By concentrating all enroute traffic into a few altitudes, this discrete altitude rule makes the enroute air traffic system less fail-safe and less fault-tolerant than it could be. The linear altitude rule proposed in this paper designates cruising altitudes as a linear function of heading or course. This rule spreads the traffic vertically and provides a default vertical separation that is proportional to path crossing angle. Monte Carlo simulation of enroute traffic with no air traffic control shows that the linear altitude rule greatly reduces both the collision rate and the mean relative speed of collisions. It also improves the efficiency of conflict resolution. It reduces the amount of altitude change required to resolve conflicts vertically, particularly for large-angle, high-speed conflicts, because those conflicts will have almost the required vertical separation by default. The inherent safety superiority of the linear altitude rule may also allow the horizontal separation standard to be reduced, which would increase airspace capacity and reduce the magnitude of speed or heading changes required to resolve conflicts horizontally.