I've heard some conflicting explanations on this topic, and I'd say the issue is twofold, or n-fold, I'm not quite sure.
Using the example of receiving the following route portion of the clearance for a departure from an uncontrolled airport: "...via direct XYZ VOR then as filed...". The VOR is to the North of the airport but the winds necessitate departing to the south. You're flying the ODP that terminates at the ABC VOR to the south, with a hold until you reach the MEA for a specified airway. Assuming ATC does not vector you off the ODP:
Two issues:
- Since going direct to the XYZ VOR takes you off-airway, would you substitute the altitude you received in your clearance for the MEA?
- Is there anything assuring terrain clearance on your direct route to the XYZ VOR? I would assume this is not ATC's responsibility as they have not vectored you at this point.
Or am I getting everything wrong and you are supposed to turn direct at 400' AGL? I believed that this was not the case unless you departed a controlled field and were "cleared for takeoff, direct XYZ VOR." However, I've also heard people say that if the airport has no DVA, and seeing as 400' is most definitely below the MVA, this is technically not a vector (even if they had said "cleared for takeoff, turn right heading xxx), and therefore you are solely responsible for obstacle clearance.
I assume you could advise the controller that you were unable to accept this clearance and request the ODP instead, but I've never encountered this personally. I would also assume that they will not be very happy with you if you tell them to standby while you pull out a sectional to figure out if complying with the clearance will take you right into the world's tallest tree. Every person I've encountered has simply done what ATC told them to do.
For day VFR conditions this really isn't that much of an issue, but these ambiguities would (for me, at least) be quite uncomfortable if departing into solid IMC.
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