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Author Topic: Navigating the LOP with the offset method.  (Read 198768 times)

Ric Gillespie

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Re: Navigating the LOP with the offset method.
« Reply #60 on: April 28, 2011, 05:30:51 AM »

All these figures seemingly look too definitive for Anglo-Saxon usance , but they are open to discussion from a fixed model ; in the other case the theory would begin with doubt in lieu of statements , the latter to more European principles the point of departure for referees.

Anglo-Saxon usance????  European principles??? 
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #61 on: April 28, 2011, 08:33:58 AM »

Or reversed , A-S scientific publications : long sentences , carefully proceed . E-publication : short sentences , definite statements. E : : Elephants eat grass. A-S : Elephants eat grass, for the period of our investigation.
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Ted G Campbell

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Re: Navigating the LOP with the offset method.
« Reply #62 on: April 28, 2011, 07:30:53 PM »

All,
Look at Kelly's aircraft performance report Page 3 item (g):  "100-150 miles out (set up a ) power glid at 250-300 fpm and maintain cruse power setting".

Why would you follow this program if you were approaching an imaginary line (an "off-set on the LOP") on a map in the cockpit?  You get there then what?  Do you then cruse along at 1000 feet eating up fuel and time trying to find your landing point.

Or do you set up a direct approach to Howland basis your navigator's instructions and when you get there, no island, say "we must be on you but can't see you"?

I would suggest the latter - straight-in approach and at a higher speed then normal cruse for the last 100-150 miles; see the discussion on the site regarding the "200 miles out and the 100 miles out time question"

Ted Campbell
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #63 on: April 29, 2011, 03:21:15 AM »

Why is it then , this head on approach  supposedly being first choice ,  that the island did not run in sight ?
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Ric Gillespie

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Re: Navigating the LOP with the offset method.
« Reply #64 on: April 29, 2011, 06:26:12 AM »

Why is it then , this head on approach  supposedly being first choice ,  that the island did not run in sight ?

(sigh)  No one knows (including you) but we do know that the RDF they were relying on for the final run in to Howland did not work.  One reasonable possibility is that they hit the advanced LOP well south of Baker ("We must be on you ...") and started searching for Howland by flying along the advanced LOP - first "up" the line, then "down" the line ("We are on the line 157 337 ..running on line ... north and south.") Running southeastward on the line was their best chance of finding land.
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Chris Owens

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Re: Navigating the LOP with the offset method.
« Reply #65 on: April 29, 2011, 10:47:31 AM »

Or reversed , A-S scientific publications : long sentences , carefully proceed . E-publication : short sentences , definite statements. E : : Elephants eat grass. A-S : Elephants eat grass, for the period of our investigation.

Obligatory old-time philosophy of science joke, entirely relevant to the question of how to assess evidence:  three philosophers are riding through Scotland in a train and look out the window to see some black sheep grazing in a pasture. The first says "Ah, I see the sheep in this district are black."  The second says, "More correctly, some of the sheep in this district are black." The third clears his throat and says, "Some of the sheep in this district are black on at least one side.."
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #66 on: April 29, 2011, 11:40:45 AM »

Very good , that is what I mean.
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Ric Gillespie

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Re: Navigating the LOP with the offset method.
« Reply #67 on: April 29, 2011, 11:52:37 AM »

Very good , that is what I mean.

You're the guy drawing firm conclusions about what happened based upon your own assumptions, many of which we have shown to be groundless. 
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #68 on: April 30, 2011, 12:03:47 AM »

Not all my own conclusions : W.L.Polhelmus , navigator @ 3rd decennium flight , 1967 , by A.Holtgren c.s. studied nav tables of the era and thinks Noonan having made an error when computing the Single Line Approach. Mechanic Koepke saw the island first from 10-12 miles away.
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #69 on: May 03, 2011, 02:05:04 AM »

T.Cmpbll . One line approaches are helpful at the end of long flights of which the accumulated error is non detectable ; because of the offset circuit plus LOP concept , no ETA can be given : TA is when the destination runs in sight below the APL. On the contrary , for a straight line flight into destination , ETA can be given on basis of known speed and distance. Good question : why did the Earhart crew not communicate "100mls out ETA 1855Z" i.l.o. "We must be on you...." at 1912Z ?
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Ted G Campbell

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Re: Navigating the LOP with the offset method.
« Reply #70 on: May 03, 2011, 07:51:41 PM »

An ETA was given at the departure of 18 hrs.  I would question why there wasn't an update along the way but either way a straight in approach seems to be the best guess.
Ted Campbell
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #71 on: May 08, 2011, 12:37:12 AM »

TG.Cmpll. For a direct flight into destination a pos.lne. , advanced or not , is of no use since @ ETA both the elevation and the azimuth of (for this case) the sun have changed since sunrise when the LOP was established. A very good navigator could attain 5% DR uncertainty at the end of a long range over ocean flight ; for a last check point at 500 mls off destination this accounts for a 12 1/2 miles radius circle of uncertainty , representing the direct approach risk of overshoot being 100% if the target visual range is less. From 1,000 ft altitude westwards the optical field width of Howland is 1 arcmin for 12.5 mls distance in clear air, this being the lower limit of resolution for the eye to form an image. No dutyful navigator would venture a direct spot on hit for Howland , with the sun ahead and early morning haze present. The "18 hrs time" @ takeoff message , btw , was not an ETA , but an assessment of duration.
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Ric Gillespie

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Re: Navigating the LOP with the offset method.
« Reply #72 on: May 08, 2011, 06:44:12 AM »

For the umpteenth time:
The intention was never to find the island by celestial and DR alone. The plan was for a direct approach using RDF. There is nothing - repeat nothing - in the literature to suggest that an offset approach was contemplated. Endlessly repeating groundless speculation does not increase its credibility. Unless you have hard evidence to offer to support your theory either give it up or take it someplace else.
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #73 on: May 08, 2011, 08:06:16 AM »

R.G. Before commencing RDF exercitions it is necessary to bring your aircraft within simultaneous radio range coverage , by DR checked celestially. I never saw a document stating that single RDF head on approach was planned , is it somewhere available ?
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Ric Gillespie

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Re: Navigating the LOP with the offset method.
« Reply #74 on: May 08, 2011, 10:24:54 AM »

R.G. Before commencing RDF exercitions it is necessary to bring your aircraft within simultaneous radio range coverage , by DR checked celestially.

Exactly.

I never saw a document stating that single RDF head on approach was planned , is it somewhere available ?

Not to my knowledge. Neither is there a statement of the intention to use an offset. Noonan's methods when navigating for Pan Am are documented in his letter to P.V.H Weems, subsequently published in Popular Aviation magazine's May 1938 issue. There is no mention using an offset.  Noonan's methods when navigating for Earhart are documented in the charts he used on the Oakland/Honlulu flight of March 17/18 1937 and the Souith Atlantic Crossing of June 7, 1937.  In neither case did he use an intentional offset.  In short, there is zero evidence that Noonan ever used an offset.  It's reasonable to suppose that he was familiar with the method but nothing to suggest that he used it on the Lae/Howland flight. Your entire theory is based upon your opinion that he SHOULD have used an offset, but arguing that something happened because it should have happened is folly. Should Earhart have set off around the world without understanding how her RDF worked?  Should Earhart and Noonan have tried to fly around the world in 1937 without knowing Morse code?  Should Fred Noonan have bet his life on the aeronautical competence of a person who had already nearly killed him in a pilot-error accident?  Harry Manning had the good sense to bail. Noonan was more desperate. In my view, to have any chance of solving the mystery of the Earhart disappearance it is essential to first grasp the staggering level of arrogance and negligence that permeated every aspect of the world flight.  The only surprise is that they got as far as they did.
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