Originally Posted by
BIRDIE
ODP's need not be part of an IFR clearance. And if you believe that an ODP is there for a case when "ATC isn't home", I would ask your explanation for a departure from a runway that includes both an ODP and a SID for a 24 hour airport. But that would be going off on a tangent. Anyway, I think I got my answer from KC10 FATboy.
I would suggest the ODP, in this case, would be for departing VFR traffic.
And no, I do not think you can assume a 3.3 degree gradient will keep you clear of obstacles if there is a published non-standard gradient for a SID.