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    'Intentional Error' Method of Navigating to Destination.
    From: Douglas Denny
    Date: 2009 Nov 10, 13:07 -0800

    Further to the Harold Gatty / Sir Francis Chichester comments:-
    I have found Gatty's book, and intended to scan the relevant bit but both the 
    scanners I have will not function. There is something wrong with Mr. Gate's 
    hated Microscoft XP operating system in my ancient computer so that it cannot 
    find the TWAIN drivers.  It's time to consider an Apple Mac as replacement.
    The mention of the 'intentional error' method is on page 70 of Harold Gatty's 
    book  "Nature is your Guide",  where he mentions using it, (written in 1957).
    It is a curious co-incidence that Gatty's flight in Siberia mentioned in his 
    book using this 'deliberate offset course to destination' method was in 1931; 
     and so was Francis Chichester's flight across the Tasman Sea in 1931, 
    (described in his book first published in 1964 - so Gatty is the first to 
    describe it in print in 1957).
    I suspect the method was a well-known 'trick' discussed at the time in 
    navigating circles of these pioneers of aerial navigation.
    I'll quote the relevant portion of Gatty's book:-
    " .... there is an additional means of straight-line navigating that is worthy 
    of mentioning here - the method of the intentional error, the method of 
    aiming (when the conditions of the journey permit) somewhat askew of the 
    final target.
    I can recall from my flying days a successful use of this simple trick.  I 
    employed it on my world flight with Wiley Post in 1931, when we were in an 
    area in which there were no distinguishable features to relate to the map.  
    The area was Eastern Siberia; and we left Irkutsk for a 'leg' of some  1100 
    miles with the intention of refuelling at a small airfield on the bank of the 
    Amur river. 
    The last several hundred miles of this leg were over Northern Muncuria - over 
    high grass country with no towns, no roads - indeed precious few distinctive 
    features of any sort.  We knew that we were unlikely to land much before dusk 
    and that the airfield was not lighted.  We could not afford to waste any time 
    looking for it.  I purposely set a course to hit the Amur river ten miles to 
    the left of our destination.  When we reached the river I told Wiley Post to 
    turn right.  We rounded a bend and there lay the airport.  We made our 
    landing with just enough light.  Wiley Post could not understand why I was so 
    definite about to turning to the right until later I explained it to him.
    There has been no check points for the last part of our route; and our maps 
    were very questionable.  If we had set a course directly to the field and had 
    missed it when we reached the Amur river, we could have used up all our 
    daylight by turning in the wrong direction......
    ..... this shows the the value of the calculated intentional error - a simple 
    method which can bring the traveler to the base line of his desired goal in 
    no doubt whatever (unless he has been guilty of a really gross 
    miscalculation) as to which way to turn.  Any normal unconscious deviation is 
    swallowed up in this intentional margin; by purposely aiming for a point 
    either to the right or to the left of his objective, the navigator eliminates 
    this uncertainty and is sure of his homefall. "
    Douglas Denny.
    Chichester.  England.
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