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RNAV SID

Asked by: 2525 views Airspace, FAA Regulations

Some RNAV DPs have a MOCA and MEA on certain segments yet some do not.

Reference KMIA  DEEEP ONE SID (RNAV):  Most of the segments have a MEA and MOCA.

Reference KCLT DEBIE SIX SID (RNAV): None of the segments have a MEA or MOCA.

Since some aircraft RNAV systems use DME/DME and DME is based upon ground stations, I am assuming the line of sight principle applies of which make sense to have a MOCA and MEA for these type of navigators. And of course there has to be a minimum altitude for GPS navigators for proper terrain/obstacle clearance and communication reception.

Question 1: Why do some RNAV DPs have a MOCA and MEA on certain segments yet some do not?

Question 2: Since a DME/ DME RNAV system can be used for the KCLT DEBIE SIX,  why is there not a MOCA or MEA ?

Thank you for the feedback.

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1 Answers



  1. Bill Trussell on Jan 29, 2014

    Your assumptions are nearly correct. First some definitions from the AIM:

    MINIMUM OBSTRUCTION CLEARANCE ALTITUDE
    (MOCA)− The lowest published altitude in effect between radio fixes on VOR airways,
    off-airway routes, or route segments which meets obstacle clearance requirements for the entire route segment and which assures acceptable navigational signal coverage only within 25 statute (22 nautical) miles of a VOR.

    Note the references to ground based radio navigation systems within a small distance from ground facilities.

    MINIMUM EN ROUTE IFR ALTITUDE (MEA)−
    The lowest published altitude between radio fixes which assures acceptable navigational signal coverage and meets obstacle clearance requirements between those fixes. The MEA prescribed for a Federal airway or segment thereof, area navigation low or high route, or other direct route applies to the entire width of the airway, segment, or route between
    the radio fixes defining the airway, segment, or route.

    Note that this definition provides not only provides navigation coverage but also obstacle clearance.

    It is noted that both of the procedures referenced in your question have a minimum initial climb gradient of at least 500 feet per NM to a minimum altitude.

    Both procedures also require Radar to be in operation for issuance and execution.

    Both procedures have segments that have MEA/MOCAs associated with them, with the last segment of the KCLT procedure being the only segment with such assignment..

    Your comment ” And of course there has to be a minimum altitude for GPS navigators for proper terrain/obstacle clearance and communication reception.” is inaccurate in one sense in that there is not a altitude requirement for GPS reception and thus no provision for any such restriction is made in these procedures. Such restrictions are intended only for ground based navigation facilities.

    In the KCLT case it is possible that the last segment of the procedure is also shared with the en route environment and thus the information would be provided based on the existence of that use in a ground based navigation scenario. The same could be said for the KMIA procedure as well.

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