Even though a date error can have the same effect on navigation as a chronometer error, it might not have been as much of a practical consideration for Noonan. As an experienced navigator, he understood the implications of using the wrong date, but for the most part in his celestial navigation experience, flights had been conducted over the course of one day, and, if the flights were overnight, it was relatively straightforward - his navigation tables were arranged such that the date progressed forward as the flight progressed.
The date in this particular case, however, was not that straightforward. In fact, the particulars of the date, time, duration, and location of Noonan and Earhart’s final flight from Lae to Howland made it an oddity in terms of celestial navigation calculations, and it may have led to a fatal error in Noonan’s calculations of where they were and where they were headed.
The Final Flight
Amelia Earhart and Fred Noonan took off from Lae, New Guinea at 10am local time on July 2nd. As they flew eastward and the Earth turned below them, the local time shifted while they covered ground. (In much the same way, if you take off on a commercial flight from San Francisco to New York, the local time shifts as you fly. If you leave at noon local time in San Francisco, you will fly for 5 hours and arrive at 8pm in New York, which is 5pm San Francisco local time, due to the time change.)
The Lae-Howland flight was estimated to take Noonan and Earhart roughly 18 hours. This schedule would have them leaving Lae at 10am local time and arriving at Howland at roughly 6am local Howland time, or 4am local time in Lae(1). During the course of the flight, they passed over midnight local time, somewhere in the middle of the Pacific Ocean. This point of local midnight is significant because at local midnight, the date would change from July 2nd to July 3rd, involving a change of date in the calculations for their local time and thus location.
If they were flying over a different part of the world, say Europe, Noonan’s calculations could be straightforward. He could continue taking celestial fixes and using the next page of charts. However, as they flew from Lae to Howland, they also crossed the International Date Line. Due to the way the Date Line and longitude lines are structured, this crossing would change their local date back to July 2nd. In effect, Earhart and Noonan took off from Lae on the morning of July 2nd at 10am local time and were set to land at Howland Island about 18 hours later on the morning of July 2nd, 1937 at 6am local time – seemingly landing 4 hours before they took off, not accounting for the time difference.
This particular set of circumstances – leaving in the late morning, heading eastward, crossing local midnight, and then subsequently crossing the International Date Line required not one, but two changes of date. This effectively required Noonan to jump back in his tables in the almanac to the previous day just after crossing the International Date Line.
If Noonan did not account for this second date change, his longitude calculations would be off by a full day, putting them 4 minutes back in terms of the sun’s right ascension, which equates to 1 degree of longitude and positions them 60 nautical miles farther eastward on their flight path than they really were, just as they were nearing their destination.
Is it possible that Noonan did not change back to July 2nd after crossing the 180-degree Date Line? This could be due to the fact that there is no alarm, warning signal, or visual reference that could have alerted him to crossing the Date Line. In fact, his chronometer was set to Greenwich Mean Time and did not imply a date change at all. They left at midnight GMT on July 2nd and were set to arrive at Howland at 1800 GMT on July 2nd. (For people in England, Earhart and Noonan's entire flight took place on July 2nd.)
The timing for these changes could also have played into human factors. They had flown all day and into the night for roughly 12-13 hours when they crossed local midnight. They then flew another five hours before crossing the Date Line at roughly 6am local time. Noonan could have been severely fatigued at the point at which he would need to change the date back to July 2nd for his calculations. He was also extremely busy. The sun would be rising shortly after they crossed the Date Line. Just before they crossed it, he may have been attempting to get his last star fixes as the morning twilight was drowning them out - and just after they crossed the Date Line, he may have been preparing to take a fix on the rising sun(1).
Earhart’s Radio Calls
While relying on Earhart’s radio calls for factual information can lead to unsubstantiated assumptions, we can look to two of her radio calls during this timeframe that might support the Date Line Theory, and answer a long-held question about the accuracy of her reports.
At 1745 GMT, Earhart is recorded as reporting her position as “about 200 miles out” from Howland Island. At 1815 GMT, Earhart is then recorded as reporting her position as “about 100 miles out” from Howland Island. Elgen Long and others have noted that she could not possibly have flown 100 miles in this 30-minute passage of time between radio calls, and many have accounted for this discrepancy by suggesting that her figures were vague estimates or a reporting of past, and not current, position fixes(1). However, a difference in longitude calculation due to a Date Line error could potentially account for this change in distance reported by Earhart over the radio.
If at 1745 GMT, Earhart was indeed about 200 miles out from Howland Island, she would have been nearing or at the International Date Line. If Noonan was using July 3rd for his calculations at this time, perhaps for a pre-sunrise star fix, then this calculation would be an accurate one and they would be truly “about 200 miles” from Howland Island. After this position fix and 1745 GMT radio call, if Noonan did not change back to the July 2nd charts, then his calculations after crossing the Date Line would put them 60 nautical farther eastward than they actually were and a star or sun fix just before Earhart’s 1815 GMT radio call may have made the difference in her now reporting “about 100 miles out” even though they actually may have been 160 miles out from Howland at the time.
These distance figures are rough estimates, by Earhart’s own admission. The radio calls are hard to put much weight on in determining what happened during the flight. There is, however, a discrepancy in the locations reported by Earhart between the two radio calls, and their crossing of the Date Line does fall between the two positions Earhart reported. This explanation may support the Date Line Theory, but may also be pure coincidence.
The Flight Path
The diagrams below show a rough estimate of Earhart and Noonan’s potential flight paths based on the Date Line Theory. The first diagram shows their path given a straight flight path to Howland Island. The second diagram shows what the flight path may have looked like if they flew a Line of Position (LOP) approach. Both flight paths ultimately result in the same conclusion. (You can click on the images to enlarge them.)
NEXT: Where is Amelia Earhart’s Electra?
1. Long, Elgen M. and Marie K. Amelia Earhart: The Mystery Solved. New York: Simon & Schuster, 1999.