NavList:

H.A.C.,

Mariners have the luxury of time to perform sight reduction following an observation. Aviators do their sight reduction ahead of time so that a fix or estimated position can be determined instantly. The high rate of aircraft speed requires this. For example a P-51 traveling over 400 kts would be 120 NM from a fix if a round of stars were observed, reduced, and plotted 18 minutes after the last observation. Having Hc altitudes pre-computed not only gives immediate results but saves the pilot the stress of performing sight reductions and flying the plane at the same time. It is much easier to do trig at a desk the day before rather than in cramped bumpy conditions during the flight. Pre-computed altitudes would have been done by Fred Noonan the day before for all the planned flight tracks.

Greg Rudzinski
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