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    Re: Running down an Astro-Position Line
    From: Gary LaPook
    Date: 2021 Mar 16, 04:01 -0700

    The purpose of positioning the plane on the LOP that runs through the destination is to be able to use that LOP as a "course line" that they can follow to the island. After you have intercepted the LOP, and turned to follow it, the navigator continues to take periodic shots and makes any corrections as necessary to stay on the LOP that runs through the destination. Chichester's last shot was at 0520 Z and even if he wanted to take such additional sights the clouds prevented any, see page 163. He spotted Balls Pyramid only 24 minutes later. Based on the slow speed of his plane, he would have travelled only about 25 NM. The usual estimate of inaccuracy in flight navigatio is 10% of the air miles covered so his position should only have deteriorated by about 2.5 NM. That was that. Once he saw the pyramid he was home free. Interestingly, it took him an additional 41 minutes to come abeam of Lord Howe so the visibility must have been very good in the direction of the Pyramid. If that big rock hadn't been there, then Chichester would have had to fly 65 minutes, say 80 NM, making the position should have been within 8 NM of the LOP plus the possible error in the observation, say 5 NM, probably good enough to spot Lord Howe.

    gl

       
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