h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Hi Phred,
You asked about Aim-Off. It was a technique attributed first to Chichester whereby the navigator deliberately places the aircraft to one side of the island then homes in on the sun LOP which he has run up from a previous sight, to pass through the destination. There is mention of it in Weems and Fred is known to have used it. There is another version of it used by the RAF about the same time which I think is less prone to error. However whichever version is used it is recommended that it is NOT used if the destination is smaller than the bandwidth error of the LOP (Howland was.)Fred would presumably have known this but reckoned that he would be ok since he would also have radio bearings, as he did finding Wake, Guam and Midway. What I would like to know is how many times, if at all, did he find these islands using celestial alone? There is also a danger of crossing to the wrong side of the island then flying AWAY from it while thinking he is going towards it. I'm sure he would have been aware of this though. Without radio it was a tall order to make that landfall...especially with Howland being in the wrong place!

nownoonan.

Yes, of course.

You make a good explanation of why Fred and Amelia would report being "running on a line 158-337" and looking for Howland using the "Off-aim" method (I've never heard it explained in those terms before), but it's basic navigation.

You may wish to look at this reference.
http://www.tighar.org/forum/FAQs/navigation.html

My theory is that Fred did get one or more crossesd LOP sun-moon fixes (and like me) failed to gmake the parallax correction. That would have led him to belive that he was 75 to 100 nautical miles further south than his actual position.

With this much error in his assumed position, he could have run back and forth for several hours without seeing tiny Howland, making minor track corrections and becoming increasingly panicked about his predicament (I assure you that in this situation panic can seriously interfere with rational thought processes). Fred would certainly have been extremely stressed about his resonsibility to Amelia, if not concerned about his own life.

Of course, I could be completely wrong. The problem could have been partial overcasts...they were running at 1,000 feet to get below clouds, inaccurate charts or many other reasons including miscommunications about radio frequencies, failures by the Itasca Captain or lack of training on radio procedure.

But eliminating the radio as a problem, Fred had the resources to find Howland with the Sun and the Moon. The LOPs from those bodies crossed perfectly on that time and that day.

On a good day I could fix my position with those bodies with an error od no more than 1-3 miles on either LOP.

And I'm not sure that I've seen any more than just speculation that his charts may have been wrong.