Mr.Lapook ,
The possibly only direct irrelevancy of the navigation model is that on the error-offset lane the sun´s altitude (16 deg) @ the erroneous turn-off-point differed considerably from the elevation (21 deg) @ the correct t-o-point , normally Noonan would have seen this . I can evade the complication (1) since when steering on the offset course the sun was below elevation (04--21) for reliable corrected sextant altitude , up to about halfway and (2) by estimating the 102 mls offset having been flown on D.R. , this last by preference . But it remains the more or less a flaw on the step of internal inconsistency . With the correct offset initial point the elevation difference was negligible (04-26 vs 04-21) for low sun given.
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Mr. van Asten,
Your diagram in your article shows that they reached the turnoff point at 1859 GMT at which point the sun's altitude was 16° 04.5' (not the 21 ° that you stated) for an observer at Howland and anywhere else on the correct LOP through Howland. This was plenty high enough for accurate sextant sights.
Anytime after 1815 GMT the sun's altitude was above the six degree minimum needed by Noonan's refraction correction table so he would have been taking sights of the sun for 44 minutes prior to the interception and would not have relied on dead reckoning for 102 miles which would have introduced an uncertainty of 10 miles in the turn off point onto the LOP. You apparently do not understand the basic idea behind the landfall procedure, that you take sights as you approach the LOP so that it is an accurate interception and then you take additional sights to ensure staying on the LOP to the destination. You do not DR for a long leg to the interception. If you were going to DR for 102 miles then there would be no reason to do the landfall procedure.
Try reading the flight manuals that explain this procedure that I have posted here:
https://sites.google.com/site/fredienoonan/topics/landfall-procedure
gl
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Mr. van Asten,
You wrote in your 2011 published paper:
"Usually the Offset
Track was fiown by OR, especially with low sun giving
less reliable position outcomes due to difficult
assess of refraction."
You correctly point out that at the point that you believe that they turned to 55° T at 1815 GMT to intercept the LOP, 102 statute miles short of your "erroneous turn off point", that the altitude of the sun was only 4° 21' which was below the minimum 6° in Noonan's refraction table so he could not take a normal sun sight at this point. You then claim that because of this that the sun continued to be too low to allow additional sights as he approached the LOP and this is, obviously, incorrect since we know the sun was 16° high at the point of interception so its altitude had to rise above 6° at some place along this leg. Even at the initial point where the turn was made to 55° T the sun rose above 6° at 1823 GMT so allowed at least 36 minutes for Noonan to take additional sights. In this period Noonan should have been able to take 5 or 6 additional sights. See:
http://www.fer3.com/arc/m2.aspx?i=116311Your theory is that due to Noonan using a marine sextant instead of the bubble sextant to determine the 175453 GMT fix that he introduced an error that caused them to be 11 NM west of where they thought they were. Your theory goes on to claim that they then dead reckoned the rest of the way to where they believed Howland was located which maintained that 11 NM error in all subsequent DR positions. This shows that you do not understand that the whole purpose of the landfall procedure is to cure any existing errors in the DR by taking additional sights while nearing the LOP and then taking additional sights while flying on the LOP to ensure staying on the LOP. Even just one sight taken after 175453 GMT would have cured the problem that you complain about since Noonan would then have a correct reading and a correct fix. Your entire DR leg, 102 SM to the turn off point plus 30 SM along the LOP is a total of 132 SM, would cause an uncertainty, due to the these DR segments, of plus and minus 13.2 SM. In addition to this uncertainty you must add the uncertainty in the original 175453 fix which is, according to all flight navigation texts and the Federal Aviation Regulations, considered to be 10 NM, 11.5 SM, making the total uncertainty, when in the vicinity of Howland, of plus and minus 24.7 SM. Nobody, in his right mind, would ever try to find this island with this level of uncertainty which is why you must take additional sights when flying the landfall procedure.
You don't have to take my word for this, you can read the standard flight navigation manuals that describe the landfall procedure here:
https://sites.google.com/site/fredienoonan/topics/landfall-proceduregl