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End-of-Navigation Points

Where each flight path would have ended at 1912 GMT

An End-of-Navigation point (EON) was identified on each path, at 1912 GMT when AE thought, and reported, she had arrived at Howland Island (1937 coordinates). The End-of-Navigation point (EON) is determined by the lateral path, vertical profile dynamics, and aircraft performance. The EON point is the commencement point for terminal search maneuvering, and construction of search grids.

Wind effects and reasonable navigation errors were then considered with terminal maneuvering to create containment zones that comprise the Primary (west) and Secondary (east) Search Grid zones.
On the two most likely Paths, Path B and C, the effects of modified winds from 20 degrees left of the nose at 18 knots (approximately 25% less velocity) were examined to produce an error tolerance for the case in which AE held a magnetic course only, with no overnight wind correction applied.

A scenario examined the effect of a wind change for the last 8.5 hours of the mission.

A second scenario examined the effect of a wind change for the final 2.0 hours.

Reduced second-half winds are supported by data from weather forecasts from Hawaii, and surface vessel weather reports in the area of the flight. Both Hawaii preflight weather forecasts contained reduced second-half mission wind velocities.

Grid Search areas are containment zones accommodating these effects, which move the End-of-Navigation point slightly east, and slightly southeast, of the original track.

Milestone waypoints for AE position reports were placed on each path at the GMT times that AE made the report, to see where on the path, in time, these might have occurred. With consideration for tolerances in reporting behavior, variance in position reporting, and error in fixing positions, the aircraft locations over the earth at the times of the reports, support validation of the analysis. This helped provide context to path construction and timing.

EON Locations
All three paths are executed based on as much factual data as possible, concluding in End-of-Navigation points at time 1912 GMT. The location of the aircraft on each path, at this time, is shown below:

Path A is the great circle direct path from Lae to Howland Island, with an EON bearing from the island 066 degrees magnetic at 22nm past the 1937 Howland Island coordinates.

N 00° 54′ 22.2W176° 21′ 33.9

Path B passes through the waypoint reported by Chater at 0519 (a point with discrepancies in location and/or time), with an EON at the 1937 Howland Island coordinates.

N 00° 49′ 00.0W176° 43′ 00.0

Path C passes through a longitude-modified 0519 GMT waypoint with an EON bearing from the island 247 degrees magnetic at 35nm short of the 1937 Howland Island coordinates.

N 00° 40′ 51.7W177° 16′ 41.1

Path Depictions
The three paths are depicted below with the time of arrival at two important AE position reports. For the 0519 GMT and 0718 GMT waypoints, the aircraft could have arrived at the waypoint before the waypoint was reported, consistent with Fred’s navigation techniques demonstrated on the Oakland to Honolulu segment, and Amelia’s reporting of Fred’s waypoints on that flight.
While the Oakland-Hawaii segment revealed FN and AE waypoint arrival and reporting techniques, the Lae to Howland segment uniquely included passage over landmasses, unlike the Oakland-Honolulu and Natal-Dakar oceanic crossings. All three paths contain over-flight of good, visible island waypoints, where checks of position, time, and fuel consumption could have been made with good precision. On these unique segments, it is possible that a position report was issued shortly after establishing the aircraft at the waypoint, approximately 10-15 minutes later, a time that also was very close to AE’s pre-scheduled reporting at 15 and 45 past the hour.

Figure 1 Flight Paths.jpg

Figure 1 - Three Possible Paths and Initial Position Reports.