Lockheed Report 487, June 4. 1936, is a very thorough and well written technical report. In addition to the assessment that report 487 is merely a marketing document, it is also a procedural guide that contains numerous recommendations for operation of the 10E. It is very similar to operations and specifications manuals that I have had to study and master over the years while transitioning into larger and more complex aircraft.
In regards to range and fuel consumption, the argument advanced that Earhart used excessive fuel en route to the LOP because the Cambridge Exhaust Gas Analyzer malfunctioned, is not convincing. The evidence put forth to support that claim is very lame and does not even rise to the level of circumstantial.
The apparent function of the instrument was to enable the pilot to precisely lean the fuel mixture for each engine. Specific Cambridge settings were calculated by Lockheed and provided to Earhart. Notwithstanding, she should have been able to lean the mixture without the instrument and if failure of the instrument did occur, she surely would not have ignored the leaning procedure.
Lockheed Report 487, Model 10E, page 3, specifies “Watch the mixture closely at all times. The engines must be run very lean,” “in climb when the power output is increased, check the mixture,“ and on page 5 and page 9, “WATCH MIXTURE AT ALL TIMES”.
Most of my flying has been with turbine engines but I do recall that in flight school while flying with piston engines, we were taught how and when to lean the fuel mixture by observing the RPM. If you lose instruments, either attitude or engine instruments, there are always options. Maybe in 1937, this was not the case.
In regards to the report by Earhart that she was flying at 1000’ altitude when on approach to Howland, not only was this so she could see the island, this let down procedure is specified in Lockheed Report 487, page 3, “When about 100 to 150 miles from the end of the flight, put the ship in a power glide losing about 250 to 300 feet of altitude per minutes while maintaining cruising power output.”
The fact that it appears that Earhart may have been trying to follow the procedures and recommendations of the manufacturer in this complex and technical report, indicates that perhaps, other than radio procedures, she might have been more astute in her approach to flying the aircraft than she has been given credit for. Perhaps not!