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    Re: Amelia Earhart's aerial navigation
    From: Ken Gebhart
    Date: 2009 Oct 29, 16:33 -0500
    I stand corrected, and did not know that Astrocompasses were used at lower latitudes.  I believe they were invented for polar use.  I am thinking that they would not be accurate to more than 5 degrees due to their small size, and that when periscopic sextants came into being, the azimuth ring in their mount would give heading checks to 1 degree.  I flew P-2s in the pacific extensively in the early 60s mainly by celnav and drift, and never saw an astrocompass.  Those were the good old days!

    On Oct 29, 2009, at 11:51 AM, Ronald P Barrett wrote:

    The Astrocompass (see pictures on www.usaf-nav-history.com ) was flown in USAF cargo planes such as the C-124 right up to the mid sexties (I have 3,000+ hours with this thing). It was and could be used on any celestial object listed in the current Ephemeries and Sight Reduction Tables (HO 249s at that time) to determine heading. Easiest was a sun reading as one got a strong shadow on it to go by. It was  a good nav aid. It required a mount and a relatively smooth flight as one had to peek through its alignment forks to get the reading.
    It is in the USAF Nav Manuals AFM 51-40s right into the 60s.
    Ron Barrett, President Air Force Navigators Observers Association ( www.afnoa.org)

    --- On Wed, 10/28/09, Paul Hirose <cfuhb-acdgw@earthlink.net> wrote:

    From: Paul Hirose <cfuhb-acdgw@earthlink.net>
    Subject: [NavList 10305] Re: Amelia Earhart's aerial navigation
    To: navlist@fer3.com
    Date: Wednesday, October 28, 2009, 11:31 PM

    Ken Gebhart wrote:
    > There is also 
    > an instrument called an Astrocompass which is used only in polar 
    > regions, and therefore not applicable on this flight.  The 
    > Astrocompass is aligned by sighting on the tail of the airplane. 

    You're right about sighting on the tail, but polar bit is wrong. An
    astrocompass would have been useful flying from island to island in the
    Pacific. It was part of the B-29 bomber navigator's kit:

    "Once in flight on the way to the [Japanese] Empire, the heading of the
    aircraft should be constantly checked by the astro-compass. It is the
    one completely accurate way of checking heading. Checking on heading
    with the astro-compass does not mean that the compass deviation on a
    heading is found once and then forgotten. Resort to the astro-compass
    should be made at frequent intervals." (XXI Bomber Command, "Combat Crew
    Manual", 1945)

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