Combined, the implementation of reduced vertical separation minima (RVSM) and uptake of Global Navigation Satellite System (GNSS) navigation, while beneficial to aviation and service provision, increase collision risk exponentially: RVSM-compliant altimetry puts an aircraft within an average of 10 m (33 ft) vertically of the assigned flight level, and GNSS puts that same aircraft within approximately 9 m (30 ft) laterally of the track centre line. Practically speaking, with these systems in place, aircraft vertically separated but operating on the same track or air traffic services (ATS) route could be in such proximity that any error or inability for either aircraft to maintain its level would create an increased probability of collision with the other.

This circular provides insight into the development of SLOP, including a brief discussion on the safety analyses and implementation considerations.

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