Hello Sonicbum
Thanks for your reply.
What you say makes perfect sense but its still not clear to me which of my 2 given interpretations are correct.
When talking about the 1000ft obstacle clearance, a positive net gradient is required.
Does this mean that:
a) obstacle clearance is 1000 ft when climbing
b) obstacle clearance can be reduced to 1000 ft if the aircraft is capable of climbing (but not necessarily doing so)
To my understanding:
When an engine fails and cruise altitude can not be maintained, you have do descent, with 2000 ft obsacle clearance. Then when reaching the driftdown altitude minimum obstacle clearance is 1000ft? 2000ft?
For the 1500ft: this is just a requirement limiting available options in diversion aerodrome (elevation)
This may be the cause of my confusion: Does the driftdown altitude assures you a positive climb gradient or is this the highest possible altitude the aircraft can maintain (level flight)?