Strategic lateral offset procedure

In addition to mitigating en route midair collision hazard, SLOP is used to reduce the probability of high-altitude wake turbulence encounters.

This hazard is an unintended consequence of RVSM vertical spacing reductions which are designed to increase allowable air traffic density.

On 13 November 2015, ICAO published a revised version of Document 4444, Pans ATM Paragraph 16.5 that includes provisions for applying SLOP in a continental/domestic air space for aircraft that are capable of offsetting in tenths of a mile.

In January 2017, the ICAO SPG (Authority for the NAT region) published updated guidance indicating that SLOP is now a requirement on the North Atlantic, rather than a recommendation.

The guidance was part of a number of changes[1] that were contained in a revised 2017 edition of NAT Doc 007:North Atlantic Airspace and Operations Manual.