Apologies in advance for the length of the post…

I was looking over the radio reports from EA after they departed Lae and found a couple of interesting observations. If we look at the log soon after they departed Lae, they gave a couple of reports with position from which we can take a rough guess at their ground speed achieved.

From what I can see, they departed Lae at 10:00am local time which was 0000 GMT.

From that Chater Report:

*The next report was received at 3.19pm (0519 GMT) on 6210 KC – “HEIGHT 10000 FEET POSITION 150.7 east 7.3 south CUMULUS CLOUDS EVERYTHING OKAY”*

If we plot these coordinates on Google Earth it is clear that she was far South of the position she should have been at if they were following the original flight plan (in reverse from the Howland to Lae flight plan calculated for them). Given that there were reports of intense storms due East of Lae at about 300 miles out, this makes perfect sense that she must have been able to avoid this storm by heading South-East then turning North East to get back to the original flight plan. The length of this journey was 257 miles from Lae on a 99.07 heading. They probably steadily climbed to 10,000ft during this segment so as to conserve fuel. For simplicity, let’s call this position check point A.

*The next report received at 5.18 pm (0718 GMT) “POSITION 4.33 SOUTH 159.7 EAST HEIGHT 8000 FEET OVER CUMULUS CLOUDS WIND 23 KNOTS”*

Let’s call this check point B. Plotting this position on Google Earth, assuming they traveled in a straight line from A to B, they would have passed directly over Nukumanu Island. This would have allowed them to measure their actual ground speed so that the head winds could be determined. Her report includes the headwinds that they measured at 23 knots which is very close to the forecasts and the observations taken that day. This may have been a very accurate measure for that point in time as well. Granted they might have changed their air speed on the journey to Howland, we can be fairly certain that she had a very good idea of the headwinds and would have adjusted her airspeed accordingly to get back to the flight plan. Another very interesting point is that when she reported this position, she was within 4 miles (off the port side) of the original flight plan vector from Lae to Howland. The heading from her previous report was 72.16, the distance was 652 miles.

There is a bit of a problem here from what I can see so far as the time stamps in the Lae radio log is concerned. The time between reports was only 2 hours yet they traveled 652 miles. For this to be true, they would have had to be traveling 326 MPH (ground speed) between check point A and check point B. This must be incorrect. If we assume that perhaps the first time stamp is incorrect but the second time stamp is correct (7 hours and 18 minutes since departing Lae), this would produce an approximate ground speed of 124.5 mph from as they progressed from Lae to check point A and then to check point B. If we now make the assumption that until check point B was encountered, and a land reference was used to estimate air speed, they were not adjusting for head winds. If we make this assumption, and we add the 23 knot head wind, this works out to an airspeed of 151 mph (at sea level), and a rough estimate of 126 mph indicated airspeed at 10,000ft (2% per 1000 feet).

If we now compare the actual flight plan to when they arrived at check point B, this was at a point about 890 miles on the original flight plan path that had assumed a ground speed of 150 mph, this works out to about 5 hours and 56 minutes en route on the original flight plan. This means that they were behind schedule, 1 hour and 22 minutes according to the original flight plan. What is also interesting here is that looking at the original flight plan, 890 miles out from Lae; they would have been in the 5 segment of the flight plan (assuming that they used the original Howland to Lae flight plan, reversed). This would have been at a point 155 miles out on a 175 mile segment. Assuming that they stayed on the same course and speed as they did from point A to point B, they would have intersected the original flight plan path in 33.2 miles or roughly within 16 minutes where the next segment in the original flight plan would begin.

I would venture to guess that for the remainder of the flight, having bypassed the storm and intercepted they original flight plan path, they would have continued on to Howland adjusting for a 23 mph head wind until some observation proved otherwise. I would also dare to guess that they would have quickly chosen a new ground speed for the remainder of the journey to Howland that they wanted to achieve and adjusted the times on the original flight plan accordingly. Since they had strayed from the original flight plan, re-calculation of the time per segment and ground speed achieved was not an option, it was a necessity.

While it is certainly possible that Fred could have recalculated the time for each segment based upon the speed actually traveled, I cannot see any compelling reason to adjust your flight plan unless navigation computations proved that you made a serious error. In order to simplify the remainder of the flight, they probably adjusted the manifold pressure and RPM as needed in order to achieve the desired ground speed at a given altitude and that they did not pore over the Lockheed documentation to re-compute optimal speeds based on the changing weight loads prior to the segment change in the flight plan. While it is entirely possible to do so, doing so could add un-necessary risks for introducing error in to the flight plan. Since they felt confident that they had enough reserves as was the case in AE's previous flights, adjusting the flight plan over and over makes little sense. They had enough on their plate, maintaining accurate timing, achieved ground speed, along with the magnetic heading on the flight plan. Fred would have also been busy looking out the window taking observations (hopefully) along the way.

If we go back to the radio log, when they were within radio range of the Itasca, the only approximate distance that we can be pretty sure of was the report at 200 miles out.

Earhart said at 1744GMT: About 200 miles out, approximately.

While this report was given around her regularly scheduled broadcast, and it would be very coincidental to be exactly 200 miles out, we can probably assuming that they were pretty close to that measure according to where they thought they were at that point in time. If we assume that this distance was approximately correct, and that they were following the original flight path, the distance traveled from check point B to this 200 miles out check point (C), this would have been approximately 1474 miles along the original flight path. If this were true, this implies that they would have achieved about a 141.3 ground speed during this segment of the flight. If they had assumed a 23 knot headwind, this would mean they indicated air speed was roughly 167.75 mph at sea level, 145 mph at 8,000ft (for the bulk of that journey). While this speed would not be ideal according to the Lockheed documentation, this would suggest that they were not adjusting their plan to optimize for gross weight and did indeed choose a fixed speed for the remainder of the trip from check point B to Howland. Perhaps the elevation of 8,000 ft was not an arbitrarily chosen altitude but was selected based on the telegram from Johnson (at Lockheed) to Lae. They just happened to find themselves at 8,000 ft at Nukumanu Island and they might have stayed there. Since they had to account for a headwind, the remainder of the recommendations (manifold pressure and RPM) would be impossible as the recommendations from Johnson must have been made for zero headwinds. One thing we can be fairly sure of is that they would experience greater efficiency at 8,000 ft than at sea level for the remainder of the flight.

As a footnote here, it is not so important that they were actually 200 miles out and headed directly for Howland, what is important is that they thought they were 200 miles out based upon following the flight plan and tracking their time. Since we know that they did not make it to Howland, we can guess at a few possible causes as to why they were not where they thought they were:

1) Inaccurate measurement of time.

2) Inaccurate magnetic course tracking.

3) Inaccurate measurement of ground speed achieved taking in to account head winds and altitude (true airspeed).

I think it is pretty safe to guess that we can rule out #1 and #2 for the most part. Tracking time is hardly debatable and following a compass heading were probably easiest tasks that they were performing.

Breaking down #3, there are perhaps a few possible scenarios:

1) Mis-calibrated or inaccurate altimeter.

2) Translations from Fred's knots per hour navigation to miles per hour needed by Earhart was incorrectly computed or Fred assumed that Earhart was performing the conversion (wouldn’t that be tragic).

3) Incorrectly accounting for head winds.

4) Computations to compute true airspeed were not computed correctly or were too course be useful.

What about a mis-calibrated altimeter? Do any of the maintenance records from Lae or previous trips suggest that the calibration was checked? Just as a guess, the readings would have had to been over 1000ft off or more to have a real impact. This seems an unlikely culprit.

Ignoring #2 as this should have been a trivial task for Noonan, accounting for head winds (#3) should have been fairly straight forward. If we assuming that they were correctly subtracting the head winds from the measured speed and Earhart reported a headwind of 23 knots at Nukumanu Island, they were probably correctly attempting to account for the headwinds (until Fred's navigation proved otherwise). If they had overestimated the headwinds, and the indications are that the winds were actually more favorable than 23 knots, the travelers would have under estimated their ground speed achieved. This would have affected when magnetic course adjustments were made. Has anyone attempted to compute how far off course the miscalculation of headwinds might have affected their estimations assuming that they were accurately tracking true air speed at altitude? This should be fairly easy to do using the actual observations compared to the 23 knots that Earhart announced. If the ground speed achieved calculation was over estimated by just 2% from check point B to Howland, this would have accounted for a 29.25 mile error by the time you reached Howland. Over estimate your ground speed by 4% and you are well over the horizon short of Howland.

As far as the computing the true air speed based on altitude goes, what was the common practice of the day? Was it typical to use charts and tables or some simple approach like 2% per 1000ft? Was there any evidence that Fred brought with him a flight computer like the E-6B that would have been available in that era to simplify the headwinds and true air speed calculations? Is there any photographic evidence that such a computer did exist?

If any of the above errors could account for a miscalculation that would have landed them outside of the 40 mile radius from Howland (over the horizon), it is probably worth speculation.

Perhaps as others have mentioned, it was perhaps a series of small miscalculations that added up to one large error. Large enough to have them miss Howland anyway. Perhaps it would be interesting to create a list of tolerance combinations (true air speed, head winds, magnetic course) that must have been held in order for them to have found Howland (within say 15 miles) without help. That may be an interesting exercise in and of itself.