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3 Answers

Direct navigation and OROCA

Asked by: 2649 views General Aviation

I have a quick question. Here's what the IPH (p.2-27) states on OROCAs:

"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-routes, random RNAV direct flights in either controlled or uncontrolled airspace. OROCAs are not subject to the same scrutiny as MEAs, MVAs, MOCAs, and other minimum IFR altitudes. Since they do not undergo the same obstruction evaluation, airport airsapce analysis procedures, or flight inspection, they cannot provide the same level of confidence as the other minimum IFR altitudes."

Given that, how do you decide your minimum IFR altitude when you file off-airway routes?

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3 Answers



  1. Mark Kolber on Jan 28, 2017

    It’s an interesting issue. Back in 1996, the Aeronautical Charting Forum, an FAA- based workgroup which reviews chart issues, began talking about this question. It went on for several years and then was dropped.

    The bottom line was (and is) that off-route navigation may only be in a radar environment and ATC will not authorize it below their MVA. So you as a pilot, are pretty much covered from both being too low due to the inability of the FAA to chart every terrain feature or obstruction in the US and being unnecessarily high because the nearest known obstruction that lead to the OROCA is 30 miles away from where you are flying.

    The Charting Forum memo is available here if you want to take a look at it: https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/afs/afs400/afs420/acfipg/media/closed/Hist%2096-01-155.pdf

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  2. Lemontree on Jan 28, 2017

    Thanks Mark. I now understand that I don’t need to worry about obstruction or traffic clearance as long as I fly off-airway routes in radar environment. But my concern is how to decide my cruise altitude to file in my flight plan with no information on a minimum IFR altitude. Would it be okay to put any number greater than OROCAs, since ATC will cover me for obstruction clearance anyway?

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  3. Best Answer


    Mark Kolber on Jan 29, 2017

    It may be helpful to think of the description of OROCA as a warranty disclaimer. “This altitude should keep you 1,000 feet above obstacles 2,000′ in mountainous terrain) in this part of the chart, but we don’t guarantee it.” Thought of it in that way, it’s a guide to safe cruising altitudes that comply with IFR requirements, as well as an emergency altitude. Yes I would feel comfortable using it as a minimums guide to the selection of a filed (meaning “requested”) cruising altitude. A planning tool.

    But I also know that OROCA altitudes can be unnecessarily high. It may be based in a feature in the northwest corner and I will be flying through the southeast. So I would also feel comfortable filing for lower than OROCA, and I have done so (although there are always special considerations for mountainous terrain). I might look at nearby airways for guidance. Might even use terrain clearance tools like those available in a number of EFBs. And cleared (meaning “assigned by ATC”) altitudes are going to be above their MVA and high enough for line of sight communications.

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