Say I want to fly off-airways (both Victor airways and T routes) for my IFR flight, direct to my destination in the US. How do I know what my off-route altitude should be so I can file for that?
I would expect this would be an altitude above the OROCA and suitable for direction of flight, however I encountered this in the Instrument Procedures Handbook:
OROCAs are intended primarily as a pilot tool for emergencies and SA. OROCAs depicted on en route charts do not provide the pilot with an acceptable altitude for terrain and obstruction clearance for the purposes of off-route, random RNAV direct flights in either controlled or uncontrolled airspace. OROCAs are not subject to the same scrutiny as MEAs, minimum vectoring altitude (MVAs), MOCAs, and other minimum IFR altitudes. Since they do not undergo the same obstruction evaluation, airport airspace analysis procedures, or flight inspection, they cannot provide the same level of confidence as the other minimum IFR altitudes.
This suggests we cannot trust the OROCA. Then I suppose the 14 CFR 91.177 indicates I need to be at least 2000 ft above the highest obstacle within 4nm of my course in mountainous areas, or 1000 in non-mountainous areas. But how do I know what this is without using OROCAs? Do we check sectional charts, or is there something more practical? Checking a sectional seems reasonable on the ground for filing, but not so if diverting in the air and flying direct to some other airport on an off-airway course not planed on the ground.
Thanks for any help!