Nesbit also believes that Earhart went in on a line about 35 miles north west of Howland Island. He bases this on the evidence of two radio transmissions received around sunrise which, be believes, show that Noonan made a fundamental error in his navigational calculations.
The clue lies in two radio messages giving her position. In the first, at 6.14am, she placed herself 200 miles from Howland Island, but in a second, sent 31 minutes later, she was only 100 miles out.
According to Nesbit, himself a trained and experienced navigator
"What many American researchers have overlooked or not realised is the significance of the two messages that were recorded around about sunrise.
This revision of position provides a very important clue to the ultimate fate of the machine and its occupants. The aircraft could not possibly have covered 100 miles in 31 minutes, even allowing for rounding up of distances."
Noonan, he explained, would have plotted his position by the stars until dawn, when he would have had to use the sun as a reference point. Marine navigators are trained to pinpoint the exact point at which the top, or upper limb, of the sun appears on the horizon.
Nesbit believes Noonan, who was trained as a marine navigator, miscalculated his position by forgetting to make a crucial adjustment for the "dip", the difference between a reading taken from the surface, and that taken from an altitude of 2,000ft.
"I think he [Noonan] was exhausted after 18 hours of flying, and simply forgot. They were probably flying up and down a line looking for the island 35 miles west of where they thought they were."
Now, it can be argued that Nesbit is making a conjecture, but it is a educated attempt, by another navigator, to explain a navigational error. Some such an error was undoubtedly made, otherwise Earhart and Noonan would have found Howland and this thread would not exist.
Earhart was not a navigator, and despite Noonan's undoubted ability he was not proficient in morse code. Neither Noonan nor Earhart had the radio expertise of Harry Manning, and it is an interesting 'what if' to imagine what might have happened had Earhart stuck with Manning.
Other posters have already alluded to the fact that the decade between Lindbergh's Paris flight and the disappearance of Amelia Earhart witnessed a transformation of aerial navigation technology and practice. A small community of innovators worked to find better tools and techniques. One of these was a Navy Lt. Commander named Phillip Van Horn Weems. He developed simplified methods of celestial navigation that, when combined with improved sextants, provided a reliable means of determining position (either a fix or a "line of position) when the sun or stars could be seen. By 1928, Weems had gone into business teaching air navigation. His initial students and clients included Charles Lindbergh, eager to find a better way than simply relying on luck to cross oceans, polar explorer Lincoln Ellsworth, and Harold Gatty, the soon-to-be-famous navigator of Wiley Post's Winnie Mae on its around-the-world record flight of 1931.
Weems also trained famous British Aviatrix Amy Johnson, seen here examining a navigational device (the caption says a drift meter) with Weems.
Weems sent the following letter to the Earhart's offering to train her in his navigational techniques.
Putnam replied
She did 'shove off' for another flight pretty soon, and we all know how it ended. I would suggest we also have a pretty good idea why it ended that way too. Such training might not have averted disaster, but it might have helped her to appreciate shortcomings in planning and equipment, and maybe even tempered a tendency to over confidence.
Cheers
Steve
Edit: The 'Hagenberger' referred to by Weems is in fact Albert H
egengerger, for those who like to google the people mentioned.