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Lost Comm’s and IFR Hemispheric Rules (91.179)

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Airspace, Instrument Rating

If flying IFR and Lost Comm's occur, do Hemispheric Rules (91.179) apply to the altitude that you fly?  For example, if flying to the east at 5000 ft. and the MEA for the route segment increases to 5500 ft. do I climb to 5500 ft. or 7000 ft?

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2 Answers



  1. Mark Kolber on Jan 30, 2021

    Neither the lost com rule nor the hemispheric rule covers it.

    The lost com rule doesn\’t talk about the hemispheric rule, and the IFR hemispheric rule in 91.179 only applies to uncontrolled airspace (it says so). ATC has its own hemispheric rule, but it is subject to modification for traffic needs, so I wouldn\’t rely on it, especially at lower IFR altitudes.

    So, we are left with the first paragraph of the AIM discussion of lost com which says to use your best judgment when encountering a situation the regs don\’t cover.

    Your judgment what to do that day in that place might be different than mine.

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  2. John D Collins on Jan 31, 2021

    I don’t think that direction of flight enters into the selection of the altitude.

    91.185 specifies (2) Altitude. At the highest of the following altitudes or flight levels for the route segment being flown:
    (i) The altitude or flight level assigned in the last ATC clearance received;
    (ii) The minimum altitude (converted, if appropriate, to minimum flight level as prescribed in Sec. 91.121(c)) for IFR operations; or
    (iii) The altitude or flight level ATC has advised may be expected in a further clearance.

    If you need to climb above the last assigned altitude and do not have been advised of an expected higher altitude , then you are suppose to use the minimum altitude for IFR operations. So if you would climb to the altitude as specified in 91.177. There is no mention of direction of flight. On an airway one would climb to the MEA or MOCA as appropriate. On a random RNAV point to point route, determining the MIA will be more difficult, but you should have IFR and VFR charts available to help determine an appropriate altitude and some EFB may provide you this information.

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