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3 degrees precession in 15 minutes… reference?

Asked by: 1516 views General Aviation

Anybody know the reference where I can find that 3 degrees precession is an acceptable amount in 15 minutes for IFR?   Thanks.

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2 Answers



  1. Fly92020 on Jul 15, 2013

    It’s a rule of thumb, not a hard & fast rule or reg. Keep in mind the Earth rotates 15-degrees an hour, so a ‘perfect’ HI is gonna precess 3.75-degrees every 15-minutes anyway, right?

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  2. Hans Mathews on Jul 19, 2013

    If you find one that only does 3 degress in 15 minutes its a keeper! I find myself making multiple significant adjustment in the first 15 minutes or so of flight and then settling into the periodic tweaking for the vacuum driven HI’s.

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