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Author Topic: Navigating the LOP with the offset method.  (Read 198495 times)

Gary LaPook

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Re: Navigating the LOP with the offset method.
« Reply #210 on: June 15, 2011, 02:14:51 AM »

The air was not still but had strong winds out of the eastern quarter. Sometimes you might get lucky and have your DR error be only 5% but most times it is not that good. If you were in Noonan's position would you assume that this is the day that your will have really good DR accuracy, since you are betting your life on it. A prudent navigator assumes a maximum possible error when working out a landfall procedure to ensure that he arrives at the island. For normal flight he might expect a 10% uncertainty but for such a critical flight he would have allowed for an even larger possible error. No flight navigator would DR for 132 SM in this situation.

You needed a flight navigator, not a sea navigator, to review your papers. Flight navigation is much different than surface navigation because the wind speed and its variations are such a large proportion of the the speed of the aircraft. A 30 knot wind is almost one-quarter the speed of Earhart's plane and a variation in speed of 10 knots is normal and 20 knots is not unusual as is the change of direction by 20  or 30 degrees. In the open ocean it is very unusual to find a current of even one knot which is only one-twentieth the speed of most ships and ocean currents are very constant, it is hard to get all that water to change direction. So DR in the air has a much greater uncertainty than sea navigation. I have copies of Mr. Noonan's charts for the Natal to Dakar flight and for the California to Hawaii flight. On the flight to Dakar the plane was off course by 125 nautical miles at one point. On the flight to Hawaii there were fixes 35, 65, 85 and 125 nautical miles off course. You have not appreciated in your papers and posts this fact of life for flight navigators.

gl

Yes , I agree on the necessity of continuous celnav check of your DR , also @ relatively short distances off destination . For the OLA , according to prescriptions by Weems et al ,   the over destination sun´s elevation is taken as the reference hc for turning off if compliance with your sextant reading is acquired . Now proceed as follows : take the sun´s elevation @ the erroneous TOP for ETA 1859 GMT, this being hc(e) = 16-00 @ 177-01-W ; 01-10-N .  Then , compute sun´s elevation for Howland @ 176-43-W ; 00-49-N (the C.Williams in mr.Noonan´s chart specified coordinates) . You will find hc(c) = 16-00 . Thence mr. Noonan , coming from the erroneous offset lane initial point (181453 GMT , 178-14-W ; 00-13-N) , will have found ho = hc @ 1859 GMT [with any sextant type] , upon which he ordered the A/c to steer 157 T on the erroneous position line , having Howland (176-38-W ; 00-48-N) @ 16 mls on the port beam , instead of below the APL , at 1912 GMT : everything with exactness to the second for arc & time according to text & diagrams of article EJN-2008 .

------------------------------------

Well, you almost have it right. At 1859 GMT Noonan takes an observation of the sun and measures 16° 00'. He then looks at his precomputed curve of the sun's altitude for 1859 GMT and sees that the precomputed altitude at the Williams coordinates at 1859 GMT is also 16° 00'. He then knows that he has intercepted the LOP through the Williams coordinates because every point on that LOP will have the same altitude for the sun as at the Williams coordinates. Nonnan then turns to 157°. See graph of precomputed altitudes available here:

 https://sites.google.com/site/fredienoonan/topics/precomputed-altitude-curves/Howlandprecomputation.jpg?attredirects=0

(The red line is the line of precomputed altitudes for the incorrect Williams coordinates and the blue line is the curve for the correct coordinates for Howland. You will notice that the spacing between the two curves remains constant, 4', which is the same as the 4 NM distance between Howland and the Williams coordinates.  Noonan did not have the correct coordinates for Howland so his graph would only have the red line. This is just a sample covering the period of 1858 to 1916 GMT. Noonan would have prepared a graph like this covering the period from 1815 to the estimated time of fuel exhaustion.)

 If, at 1859 GMT Noonan had measured only 15° 52' he would see the difference between his measurement and the expected measurement of 16° 00' found on the red curve equals 8' so he would know that he had not yet reached his turn off point but that he still had an additional 8 nautical miles to go. Any altitude measurement that plots below the curve means that the plane has not yet reached the LOP and must continue toward the northeast. Any sextant altitude measurement that plots above the curve means that the plane has overshot the LOP so the plane must correct its heading back toward the southwest.

After he has turned to 157° he continues to take sextant readings. For example, if he takes a reading at 1907 GMT and finds an altitude of 17° 52' and he compares it to the red line for the same time and reads out 17° 50' he would see that the difference is 2' indicating that he is 2 NM to the left of course since his reading is greater than the correct altitude. He could then make a slight heading change to the right or just ignore it since a 2' difference is very small and well within the expected scatter of the sextant readings. This shows him tracking closely to the LOP that leads to the Williams coordinates. The LOP through the Williams coordinates runs parallel to the correct LOP through Howland, offset to the southwest by 4 NM.

Then at 1912 GMT he takes another sextant shot of the sun and measures 18° 58' and comparing it to the precomputed altitude on the red line for the same time and takes out the same number, 18° 58' which shows he is on the LOP through the Williams coordinates. Staying on this LOP will take the plane over  the Williams coordinates.

Since the Williams coordinates are only 4 NM from Howland the plane will pass within 4 NM of Howland not the 16 miles that you stated. He will not have turned off too soon because his sextant reading has cured the error in the 175453 fix.

gl
« Last Edit: June 15, 2011, 11:57:47 PM by Gary LaPook »
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Monty Fowler

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Re: Navigating the LOP with the offset method.
« Reply #211 on: June 15, 2011, 11:52:02 AM »

It seems to me that Gary is making an awful lot of sense, not to mention his Been There, Done That level of experience that he brings to the discussion.

Which, again to me, carries a whole lot more weight than repeatedly throwing numbers against the wall to see which ones stick. My 2 cents.
Ex-TIGHAR member No. 2189 E C R SP, 1998-2016
 
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Chris Owens

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Re: Navigating the LOP with the offset method.
« Reply #212 on: June 15, 2011, 11:52:25 AM »

I'm going to ask Marty to chime in due to his superior knowledge of Jesuit teachings, but if I recall correctly they teach you in middle school that this type of discussion can make you go blind.

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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #213 on: June 15, 2011, 01:37:07 PM »

Well, you almost have it right. At 1859 GMT Noonan takes an observation of the sun and measures 16° 00'. He then looks at his precomputed curve of the sun's altitude for 1859 GMT and sees that the precomputed altitude at the Williams coordinates at 1859 GMT is also 16° 00'. He then knows that he has intercepted the LOP through the Williams coordinates because every point on that LOP will have the same altitude for the sun as at the Williams coordinates. Nonnan then turns to 157°. See graph of precomputed altitudes available here:

 https://sites.google.com/site/fredienoonan/topics/precomputed-altitude-curves/Howlandprecomputation.jpg?attredirects=0

(The red line is the line of precomputed altitudes for the incorrect Williams coordinates and the blue line is the curve for the correct coordinates for Howland. You will notice that the spacing between the two curves remains constant, 4', which is the same as the 4 NM distance between Howland and the Williams coordinates.  Noonan did not have the correct coordinates for Howland so his graph would only have the red line.)

 If, at 1859 GMT Noonan had measured only 15° 52' he would see the difference between his measurement and the expected measurement of 16° 00' found on the red curve equals 8' so he would know that he had not yet reached his turn off point but that he still had an additional 8 nautical miles to go. Any altitude measurement that plots below the curve means that the plane has not yet reached the LOP and must continue toward the northeast. Any sextant altitude measurement that plots above the curve means that the plane has overshot the LOP so the plane must correct its heading back toward the southwest.

After he has turned to 157° he continues to take sextant readings. For example, if he takes a reading at 1907 GMT and finds an altitude of 17° 52' and he compares it to the red line for the same time and reads out 17° 50' he would see that the difference is 2' indicating that he is 2 NM to the left of course since his reading is greater than the correct altitude. He could then make a slight heading change to the right or just ignore it since a 2' difference is very small and well within the expected scatter of the sextant readings. This shows him tracking closely to the LOP that leads to the Williams coordinates. The LOP through the Williams coordinates runs parallel to the correct LOP through Howland, offset to the southwest by 4 NM.

Then at 1912 GMT he takes another sextant shot of the sun and measures 18° 58' and comparing it to the precomputed altitude on the red line for the same time and takes out the same number, 18° 58' which shows he is on the LOP through the Williams coordinates. Staying on this LOP will take the plane over  the Williams coordinates.

Since the Williams coordinates are only 4 NM from Howland the plane will pass within 4 NM of Howland not the 16 miles that you stated. He will not have turned off too soon because his sextant reading has cured the error in the 175453 fix.

The correct TOP was @ 176-53 ; 01-13 , the erroneous TOP was @ 177-01 ; 01-10 according to EJN-2008 . With H.O.208 we find for 1859 GMT / Hwl. ass.posn. hc = 15-12´.0 . For the error TOP we also find 15-12´.0 , which says that mr.Noonan observed ho = hc  @ 1859 GMT to alter to 157 T on the erroneous LOP . There is however , more : when approaching for the TOP on the correct offset lane , A/c also met the error LOP @ a point X, slightly southeastward of the error TOP . Elevation of sun on that point will be close to 15-12´ and it is therefore possible that the island was missed  since the computations for elevation had been made by H.O.208 in combination with the erroneous Howland chart coordinates. I will for X-point additionally compute with H.O.208 , if  elevation of sun is close to 15-12´ these outcomes may open new vistas in accordance with Occam´s razor : with observance of all in and outs : simplest solution.
« Last Edit: June 15, 2011, 03:58:09 PM by Martin X. Moleski, SJ »
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #214 on: June 15, 2011, 03:03:13 PM »

Well, since we do not have Mr. Noonan"s work papers, we have only your theoretical computations of them, how about producing at least one other example of anybody other than Noonan using your "sunrise/sunset" methodology or a cite to a navigation text describing your method?

Not needed , Noonan himself is the example , by his sunset fix 071930 GMT .
« Last Edit: June 15, 2011, 03:58:37 PM by Martin X. Moleski, SJ »
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Chris Johnson

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Re: Navigating the LOP with the offset method.
« Reply #215 on: June 15, 2011, 03:42:52 PM »

PLEASE can someone apart from GLP or HVA give us an update as to where this thread is going!

:) i'm not a navigator but the word circule (sp) comes to mind :)
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Bruce Burton

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Re: Navigating the LOP with the offset method.
« Reply #216 on: June 15, 2011, 03:47:33 PM »

....if I recall correctly they teach you in middle school that this type of discussion can make you go blind.

At the very least, go deaf.  :P  After a year, this thread with its 215 replies and 6,591 views has only become more and more convoluted. It would seem we've squeezed out all the goodness that's in here; maybe, we should leave the dead horse in peace.  :'(
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Alex Fox

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Re: Navigating the LOP with the offset method.
« Reply #217 on: June 15, 2011, 04:05:36 PM »

R.I.P. dead horse.   :'(
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Martin X. Moleski, SJ

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Re: Navigating the LOP with the offset method.
« Reply #218 on: June 15, 2011, 04:16:15 PM »

....if I recall correctly they teach you in middle school that this type of discussion can make you go blind.

Stuff happens!

At the very least, go deaf.  :P  After a year, this thread with its 215 replies and 6,591 views has only become more and more convoluted. It would seem we've squeezed out all the goodness that's in here; maybe, we should leave the dead horse in peace.  :'(

I gave up on participating in this discussion in detail a couple of weeks ago after someone provided links to Van Asten's two articles.

Gary's posts have been illuminating.  I suppose at some point we could lock the thread and ask them to carry on the rest of the argument in private.  
LTM,

           Marty
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Gary LaPook

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Re: Navigating the LOP with the offset method.
« Reply #219 on: June 15, 2011, 06:14:06 PM »

....if I recall correctly they teach you in middle school that this type of discussion can make you go blind.

Stuff happens!

At the very least, go deaf.  :P  After a year, this thread with its 215 replies and 6,591 views has only become more and more convoluted. It would seem we've squeezed out all the goodness that's in here; maybe, we should leave the dead horse in peace.  :'(

I gave up on participating in this discussion in detail a couple of weeks ago after someone provided links to Van Asten's two articles.

Gary's posts have been illuminating.  I suppose at some point we could lock the thread and ask them to carry on the rest of the argument in private. 

--------------------------------

You don't have to, I'm done. I thought I was finally making some progress, but it's clear I wasn't.

 I first communicated with Mr. van Asten after I read his two articles that are just full errors. I was making a friendly effort to help him understand how this navigation really works.  I think that it is obvious to everyone that he is not interested in learning anything. He always goes back to his 0719:30 observation, the one that led to the position report that was received in Lae one  minute and a half prior to that observation! I was always taught that time goes in only one direction, from earlier to later. Apparently in Mr. van Asten's parallel universe time can run in the opposite direction.  Don't try to confuse him with the facts.

So, I give up, he will have to carry on without my help.

gl
« Last Edit: June 15, 2011, 07:12:48 PM by Gary LaPook »
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Martin X. Moleski, SJ

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Re: Navigating the LOP with the offset method.
« Reply #220 on: June 15, 2011, 06:23:17 PM »

You don't have to, I'm done.

I first communicated with Mr. van Asten after I read his two articles that are just full errors. I was making a friendly effort to help him understand how this navigation really works.  I think that it is obvious to everyone that he is not interested in learning anything. He always goes back to his 0719:30 observation, the one that lead to the position report that was received in Lae one  minute and a half prior to that observation! I was always taught that time goes in only one direction, from earlier to later. Apparently in Mr. van Asten's parallel universe time can run in the opposite direction.  Don't try to confuse him with the facts.

So, I give up, he will have to carry on without my help.

I appreciate your efforts very much, Gary.  Thanks!
LTM,

           Marty
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Gary LaPook

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Re: Navigating the LOP with the offset method.
« Reply #221 on: June 15, 2011, 07:16:53 PM »

You don't have to, I'm done.

I first communicated with Mr. van Asten after I read his two articles that are just full errors. I was making a friendly effort to help him understand how this navigation really works.  I think that it is obvious to everyone that he is not interested in learning anything. He always goes back to his 0719:30 observation, the one that lead to the position report that was received in Lae one  minute and a half prior to that observation! I was always taught that time goes in only one direction, from earlier to later. Apparently in Mr. van Asten's parallel universe time can run in the opposite direction.  Don't try to confuse him with the facts.

So, I give up, he will have to carry on without my help.

I appreciate your efforts very much, Gary.  Thanks!
------------------------------

I hope that it wasn't a complete waste of my time. Hopefully my long explanations have served to demystify the process for other readers of these posts so that they can see now that it isn't voodoo or even rocket science. It has some complications but it is a rational process when you see how it all works.

gl
« Last Edit: June 15, 2011, 11:49:26 PM by Gary LaPook »
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #222 on: June 15, 2011, 10:47:45 PM »

You don't have to, I'm done.

I first communicated with Mr. van Asten after I read his two articles that are just full errors. I was making a friendly effort to help him understand how this navigation really works.  I think that it is obvious to everyone that he is not interested in learning anything. He always goes back to his 0719:30 observation, the one that lead to the position report that was received in Lae one  minute and a half prior to that observation! I was always taught that time goes in only one direction, from earlier to later. Apparently in Mr. van Asten's parallel universe time can run in the opposite direction.  Don't try to confuse him with the facts.

So, I give up, he will have to carry on without my help.

I appreciate your efforts very much, Gary.  Thanks!
------------------------------

I hope that it wasn't a complete wasted of my time. Hopefully my long explanations have served to demystify the process for other readers of these posts so that they can see now that it isn't voodoo or even rocket science. It has some complications but it is a rational process when you see how it all works.

gl

The 0718 time point is not from a radio logbook and nowhere cited , unless in the Chater report . It is even possible if not probable , for the case that the announce was made @ 0718 in lieu of 0720 , that mr.Noonan saw his series of observations before sunrise nearing the precomputed hc-ho graph or listing upon which he messaged to the pilot in advance . I do not believe this scenario , but the possibility remains.
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #223 on: June 15, 2011, 11:05:17 PM »

You don't have to, I'm done.

I first communicated with Mr. van Asten after I read his two articles that are just full errors. I was making a friendly effort to help him understand how this navigation really works.  I think that it is obvious to everyone that he is not interested in learning anything. He always goes back to his 0719:30 observation, the one that lead to the position report that was received in Lae one  minute and a half prior to that observation! I was always taught that time goes in only one direction, from earlier to later. Apparently in Mr. van Asten's parallel universe time can run in the opposite direction.  Don't try to confuse him with the facts.

I highly appreciated your professional comments & inputs really of great value but , i.m.h.o. they are not convincing in the field of the deployed theory . Too bad that no other quantitative inquiry exists for comparison .

So, I give up, he will have to carry on without my help.

I appreciate your efforts very much, Gary.  Thanks!
------------------------------

I hope that it wasn't a complete wasted of my time. Hopefully my long explanations have served to demystify the process for other readers of these posts so that they can see now that it isn't voodoo or even rocket science. It has some complications but it is a rational process when you see how it all works.

gl
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #224 on: June 16, 2011, 02:13:34 AM »

The air was not still but had strong winds out of the eastern quarter. Sometimes you might get lucky and have your DR error be only 5% but most times it is not that good. If you were in Noonan's position would you assume that this is the day that your will have really good DR accuracy, since you are betting your life on it. A prudent navigator assumes a maximum possible error when working out a landfall procedure to ensure that he arrives at the island. For normal flight he might expect a 10% uncertainty but for such a critical flight he would have allowed for an even larger possible error. No flight navigator would DR for 132 SM in this situation.

You needed a flight navigator, not a sea navigator, to review your papers. Flight navigation is much different than surface navigation because the wind speed and its variations are such a large proportion of the the speed of the aircraft. A 30 knot wind is almost one-quarter the speed of Earhart's plane and a variation in speed of 10 knots is normal and 20 knots is not unusual as is the change of direction by 20  or 30 degrees. In the open ocean it is very unusual to find a current of even one knot which is only one-twentieth the speed of most ships and ocean currents are very constant, it is hard to get all that water to change direction. So DR in the air has a much greater uncertainty than sea navigation. I have copies of Mr. Noonan's charts for the Natal to Dakar flight and for the California to Hawaii flight. On the flight to Dakar the plane was off course by 125 nautical miles at one point. On the flight to Hawaii there were fixes 35, 65, 85 and 125 nautical miles off course. You have not appreciated in your papers and posts this fact of life for flight navigators.

gl

Yes , I agree on the necessity of continuous celnav check of your DR , also @ relatively short distances off destination . For the OLA , according to prescriptions by Weems et al ,   the over destination sun´s elevation is taken as the reference hc for turning off if compliance with your sextant reading is acquired . Now proceed as follows : take the sun´s elevation @ the erroneous TOP for ETA 1859 GMT, this being hc(e) = 16-00 @ 177-01-W ; 01-10-N .  Then , compute sun´s elevation for Howland @ 176-43-W ; 00-49-N (the C.Williams in mr.Noonan´s chart specified coordinates) . You will find hc(c) = 16-00 . Thence mr. Noonan , coming from the erroneous offset lane initial point (181453 GMT , 178-14-W ; 00-13-N) , will have found ho = hc @ 1859 GMT [with any sextant type] , upon which he ordered the A/c to steer 157 T on the erroneous position line , having Howland (176-38-W ; 00-48-N) @ 16 mls on the port beam , instead of below the APL , at 1912 GMT : everything with exactness to the second for arc & time according to text & diagrams of article EJN-2008 .

------------------------------------

Well, you almost have it right. At 1859 GMT Noonan takes an observation of the sun and measures 16° 00'. He then looks at his precomputed curve of the sun's altitude for 1859 GMT and sees that the precomputed altitude at the Williams coordinates at 1859 GMT is also 16° 00'. He then knows that he has intercepted the LOP through the Williams coordinates because every point on that LOP will have the same altitude for the sun as at the Williams coordinates. Nonnan then turns to 157°. See graph of precomputed altitudes available here:

 https://sites.google.com/site/fredienoonan/topics/precomputed-altitude-curves/Howlandprecomputation.jpg?attredirects=0

(The red line is the line of precomputed altitudes for the incorrect Williams coordinates and the blue line is the curve for the correct coordinates for Howland. You will notice that the spacing between the two curves remains constant, 4', which is the same as the 4 NM distance between Howland and the Williams coordinates.  Noonan did not have the correct coordinates for Howland so his graph would only have the red line. This is just a sample covering the period of 1858 to 1916 GMT. Noonan would have prepared a graph like this covering the period from 1815 to the estimated time of fuel exhaustion.)

 If, at 1859 GMT Noonan had measured only 15° 52' he would see the difference between his measurement and the expected measurement of 16° 00' found on the red curve equals 8' so he would know that he had not yet reached his turn off point but that he still had an additional 8 nautical miles to go. Any altitude measurement that plots below the curve means that the plane has not yet reached the LOP and must continue toward the northeast. Any sextant altitude measurement that plots above the curve means that the plane has overshot the LOP so the plane must correct its heading back toward the southwest.

After he has turned to 157° he continues to take sextant readings. For example, if he takes a reading at 1907 GMT and finds an altitude of 17° 52' and he compares it to the red line for the same time and reads out 17° 50' he would see that the difference is 2' indicating that he is 2 NM to the left of course since his reading is greater than the correct altitude. He could then make a slight heading change to the right or just ignore it since a 2' difference is very small and well within the expected scatter of the sextant readings. This shows him tracking closely to the LOP that leads to the Williams coordinates. The LOP through the Williams coordinates runs parallel to the correct LOP through Howland, offset to the southwest by 4 NM.

Then at 1912 GMT he takes another sextant shot of the sun and measures 18° 58' and comparing it to the precomputed altitude on the red line for the same time and takes out the same number, 18° 58' which shows he is on the LOP through the Williams coordinates. Staying on this LOP will take the plane over  the Williams coordinates.

Since the Williams coordinates are only 4 NM from Howland the plane will pass within 4 NM of Howland not the 16 miles that you stated. He will not have turned off too soon because his sextant reading has cured the error in the 175453 fix.

gl

No , the ho values acquired are the same H.O.no.208 hc = 15-12´ for as well the LOP over Howland T.P. , Howland A.P. and TOP-error , the last having been met first by A/c . Thence @ 1912 GMT A/c passed 16 mls west of Howland T.P.
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