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    Re: Sights perpendicular to course
    From: Gary LaPook
    Date: 2014 Nov 6, 18:41 -0800
    The standard names for these types on observations in flight navigation are "speed line" and "course line." All in flight celestial "fixes" are actually running fixes because the observations are usually spaced four minutes apart during which the plane (such as a Boeing 707 or B-52, etc) will cover 32 NM. Since you normally shoot three stars you actually end up advancing the first shot for 8 minutes, 64 nm in a jet. The usual method is to shoot the "course line" out by the wingtip first since advancing it introduces less uncertainty in the fix. Then you shoot the "speed line" on a star if front of you, or behind you. See:

    A friend who was a flight navigator for PanAm sent me this:

     At Pan American, it was standard practice to take three celestial shots to form a triangle at to the most probably position. It also backed up the first two. Generally we would shoot the course line first, a the speed line next, and a 45 degrees angle last. In the 707, we used 8 nm a minute to advance or retard the lines. Didn't bother with ground speed. Shots were every four minutes, so advances were 32 nm either forward, or backward. We were well aware of the single line procedure for arriving at a destination, but of course never needed to use it. 

    Also see:


    From: Frank Reed <NoReply_FrankReed@fer3.com>
    To: garylapook@pacbell.net
    Sent: Thursday, November 6, 2014 4:36 PM
    Subject: [NavList] Sights perpendicular to course

    What would you call celestial sights taken as nearly as possible perpendicular to the current course, and also what would you call sights taken parallel to the current course? I'm just looking for appropriate adjectives here, so suggestions are welcome. If we do a running fix and one of the LOPs is parallel to the course made good then there's no need to advance the LOP since the advanced line is the same as the original. Running fixes are then trivial. Or is there a name for that??

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