Usually only applicable this in airspace when you are >3000ft, (but below 10,000ft) Requirement to maintain 1000ft above and below clouds, 5km forward visibility and 1500m horizontally away from clouds. Owing the prevalence of controlled airspace, VFR on top is often only an option on longer transits over large bodies of water (e.g. English channel crossing pictures above ) or over some low level hilly/mountainous terrain where being above and well clear of any cloud is safer than attempting to navigate visually low level in undulating terrain.