NavList:

But CN is a "position finding" system, not a "position keeping" system so the accuracy of  a celestial fix is completely independent of prior fixes or DR errors. You can start  with three observations and know only that you are on the planet Earth and in only three iterations come up with a fix of normal accuracy. Noonan could have paddled a canoe across the Pacific to Howland and the final LOP used to find the island would be of normal accuracy. Dead reckoning ,  INS and Doppler  are "position keeping" systems so they acquire errors or uncertainty as time goes by. CN, GPS, LORAN, CONSOL, DECCA, VOR, visual bearings, and radio bearings are all  "position finding" systems. Interestingly, OMEGA has characteristics of both. OMEGA gives you an LOP within a "lane" but you must keep account of crossing the lanes to place the LOP within the correct lane. The normal way to do a single LOP landfall is to use the destination as the AP so if you want to plot the LOPs (which is not really necessary) then the LOPs get more accurate as you approach the island. The only impact of deterioration of the DR on a long leg is that one must aim off farther to the side to intercept the LOP through destination so that you can be certain on what side of the destination you intercept the LOP. Noonan would have known when he had his last fix and would have allowed for DR uncertainty commensurate with the length of the DR leg.

gl



Greg R. wrote:

a very experienced flight navigator, such as Fred Noonan,
should have been able to find anl island, such as Howland.
    

True enough - and while not wanting to disagree with your analysis, I'm not sure it's a valid comparison.

Your flights had the benefit of a very recent and very close known position (i.e. Oxnard or Santa Paula airports, depending on where you departed from) that Earhart and Noonan didn't after 20-some hours over the open ocean.

I would certainly hope that any halfway-decent navigator would be able to find an island (or at least an LOP through it) that's only a few tens of miles offshore with that as a starting point...  ;-)

--
GregR



--- On Wed, 1/13/10, Gary LaPook <glapook@pacbell.net> wrote:

  

From: Gary LaPook <glapook@pacbell.net>
Subject: [NavList] Re: Cessna CN Summary
To: NavList@fer3.com
Date: Wednesday, January 13, 2010, 12:55 PM
Even first timer flight navigators
taking  sights achieved the accuracy needed to find an
island. So,a very experienced flight navigator, such as Fred
Noonan, should have been able to find anl island, such as
Howland.

gl

gregrudzinski@yahoo.com
wrote:
    

Three Flights Completed

Five Sun observations performed using a two minute
      

averager
    

( Intercepts of 2A, 3A, 8A, 10A, 18A )

Six individual observations performed with four
      

consecutively averaged.
    

( Average of four 9A, Individual from back seat 22T,
      

Individual from front seat 19T )
    

First Impression- The Bubble moves a great deal even
      

though the plane seems to be level and steady. This was most
apparent when the horizon prism was flipped in on the MK 5
where the bubble movement could be seen relative to the
horizon. In spite of this reasonable accuracy was still
obtained. Clearly there would have been no problem finding
an island such as Anacapa (6NM long) with or without an
averager but given the choice I would go with the averager.
    

Greg Rudzinski



      

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