Originally Posted by
Uplinker
No help but just a comment; In the days before improved IRSs with GPS; aircraft were "scattered" either side of oceanic airways, owing to poorer navigational accuracy - resulting in random lateral offsets. It is the improved accuracy and reliability of laser ring gyro IRSs coupled with GPS that makes track keeping so much more accurate and therefore SLOP sometimes desirable.
If you unofficially applied SLOP of just 1 or 2 nm over the Ocean, who is going to either notice or care? (as long as you remember to cancel the SLOP after the crossing).
ATC will notice and will certainly care. If in surveillance coverage, e.g. ADS-B, ATC will see you off track on their screens and challenge you. Even out of surveillance, the periodic automatically downlinked ADS-C position reports (which will report the aircraft is somewhere other than its filed/cleared route) will generate route conformance warnings to ATC, who again will challenge what you are doing. Being off route can stuff up lateral separation very quickly, given the larger lateral tolerances applied to tracks in oceanic airspace.
Regarding improved navigational accuracy - true. This has flowed through to non-surveillance ATC separation standards so that reduced tolerances can be applied to suitably equipped aircraft with commensurately qualified crew.