JW,
Overlooked including OPS 1.542 in my last post.
OPS 1.542 - En-route — Single-engine aeroplanes.
(a) An operator shall ensure that the aeroplane, in the meteorological conditions expected for the flight, and in the event of engine failure, is capable of reaching a place at which a safe forced landing can be made. For landplanes, a place on land is required, unless otherwise approved by the Authority.
(b) When showing compliance with subparagraph (a) above:
1. the aeroplane must not be assumed to be flying, with the engine operating within the maximum continuous power conditions specified, at an altitude exceeding that at which the rate of climb equals 300 ft per minute; and
2. the assumed en-route gradient shall be the gross gradient of descent increased by a gradient of 0,5 %.
Additionally two-engine aeroplanes unable to satisfy the climb requirements under appendix 1 to 1.525(b) shall be treated as single-engine aeroplanes (OPS 1.525(b)).