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    Re: I.C. and sunspot
    From: Brian Walton
    Date: 2019 May 13, 20:36 -0700

    Frank’s post shows an aircraft condensation trail, and reminds me of a CN position  I got years ago.

    Before scientific calculators and GPS were available to me, I got a short-notice chance to join a yacht ferrying from Dubrovnik to St Lucia. The skipper was a Russian trained Yugoslav, and used a quick reduction method based on 2 triangles, and an assumed position, but written in a language foreign to me.  I was number 2, using my current Reed’s versine method, which the skipper thought out-dated, although the results were the same. His plotting method used exercise book printed lines, and I have used it ever since.  We took watches in turn, either handling the yacht, or navigating.

    A few days out of Gibraltar, heading for Tenerife, the visibility was too poor for CN, the log was not working, and we were approaching the shipping lanes running through the Canaries with our position somewhat uncertain. The skipper was navigating, and my watch was steering.  He was a little wary of me, since he was a supertanker operator, and knew I had blown one of those up a few years before.

    I suddenly announced from on deck, that our destination was 99 miles away, and 10 degrees starboard. He scurried below, and came back saying “You right! How you know that?”. I had been watching condensation trails off to the right, and knew they were B 737s ( they were safer then) which cruised at 33,000’.  I also knew that the outer marker for Tenerife South (TFS) was close to our offshore waypoint for Los Christianos.  B737s, before glass cockpits, started their descent at a range of 3 times their height in thousands, i.e. 3x33, and the start of descent was where they throttled back, and the contrails suddenly stopped.

    We got along fine after that.

    Brian Walton

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