Amelia Earhart Search Forum > Celestial choir
LOP-Possible stupid question
Chris Johnson:
--- Quote from: h.a.c. van asten on August 18, 2011, 12:04:19 PM ---First and evidently the recorded aircraft progression line did not by far cover the sun line as advanced over Howland´s true coordinates , secondly an on board compass pointing flight in any direction including north gives no resolution of the coordinates you are over .
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I'll use an example from compass navigation on land. In poor visability and using a map where I have some idea (like FN said with his LOP) I can follow a bearing that gets me to my destination or there abouts!
If the LOP was correct then why not just fly along the line?
Good question about the auto pilot, nether thought of that.
Gary LaPook:
--- Quote from: Chris Johnson on August 18, 2011, 12:34:04 PM ---
--- Quote from: h.a.c. van asten on August 18, 2011, 12:04:19 PM ---First and evidently the recorded aircraft progression line did not by far cover the sun line as advanced over Howland´s true coordinates , secondly an on board compass pointing flight in any direction including north gives no resolution of the coordinates you are over .
--- End quote ---
I'll use an example from compass navigation on land. In poor visability and using a map where I have some idea (like FN said with his LOP) I can follow a bearing that gets me to my destination or there abouts!
If the LOP was correct then why not just fly along the line?
Good question about the auto pilot, nether thought of that.
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"Or there abouts" is not close enough to find an island. Quick, what direction should I fly to get to Chicago? You can't answer that question because the answer depends upon where I am starting from. If in New York I should head west; if in New Orleans I must head north, etc. The accuracy of the position determined by this dead reckoning (just following a compass heading) can never be more accurate that the accuracy at which you knew your starting position and Noonan obviously did not have a high accuracy starting position or else he would have landed on Howland. The "follow the compass bearing" only works if you know where you are starting from. But even if he knew exactly where he was, directly over Howland, and he wanted to fly to Gardner (the course is actually 159° true, not 157°) and he turned to that course then the accuracy of his position degrades at a rate of 10% of the distance flown so by the time he got in the vicinity of Gardner after flying 350 NM his position would be uncertain by up to 35 NM to the east and to the west of Gardner, a band 70 NM wide. Would you bet your life on this chance?
See: https://sites.google.com/site/fredienoonan/topics/accuracy-of-dead-reckoning
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You cannot determine if you are staying on the course line that would take you to Niku because the azimuth of the line changes as the sun moves (the LOP pivots on Howland island) and doesn't go anywhere near Niku later in the day.
See: https://sites.google.com/site/fredienoonan/discussions/why-it-was-not-possible-to-follow-lop-to-nikumaroro
gl
Chris Johnson:
Ok simplistic idea here!
You think you are on the LOP and will either fly over the Howland area or the Phoenix area. You fly North South in the hope its Howland, Baker, Jervis but its not its Gardner er al. Possible? I don't know but could it have been?
Gary LaPook:
--- Quote from: Chris Johnson on August 18, 2011, 05:44:01 AM ---I hold my hands up and admit that I am no navigator but have a question regarding the LOP that I hope doesn’t become another theory battle between our esteemed navigational colleagues.
I may have asked something similar before so be patient.
FN and AE miss Howland Island but FN’s observations and calculations say he has reached the LOP 157 – 337. How wide/broad is this line for them to fly up/down? Could AE not just watch a compass to stay on the LOP with FN then taking shots to adjust for wind etc?
In this way could they then not reach the ‘catchers mitt’ of the Phoenix island?
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You have to allow for the possibility of up to a 7 NM uncertainty in an LOP derived from a sextant observation. This means you may be up to 7 NM to the right or to the left of the LOP that you believe should take you to Howland so the possible error band in 14 NM wide. However, you are much more likely to be closer to the center of the error band than to either edge but you must allow for that maximum possible error in planning your approach. If they did perfect navigation then following the LOP should have taken Noonan directly over Howland. If, at the moment they were passing Howland, the error was at maximum then they might have passed up to 7 NM east or west of the island, so Howland would have been easily visible with 20 NM visibility.
There is the possibility that Noonan was using coordinates for a point about 5 NM west- north west of he island and this would have produced an LOP that was offset from the proper LOP by 4 NM. Following this erroneous LOP would cause the plane to fly by Howland within a 14 NM error band centered 4 NM to the west of the island. So looking at the worst case, flying the 4 NM offset LOP and being at the furthest error to the west, another 7 NM, then the plane could have been passing the island offset by, at most, 11 NM, again well within visibility range.
gl
Gary LaPook:
--- Quote from: Chris Johnson on August 18, 2011, 02:37:01 PM ---Ok simplistic idea here!
You think you are on the LOP and will either fly over the Howland area or the Phoenix area. You fly North South in the hope its Howland, Baker, Jervis but its not its Gardner er al. Possible? I don't know but could it have been?
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Read:
https://sites.google.com/site/fredienoonan/discussions/why-it-was-not-possible-to-follow-lop-to-nikumaroro
gl