Does anyone still use the hp41 airborne?

[Geoff Quickfall]

(01-28-2014 01:42 AM)twdeckard Wrote:  I have a question. In your video you mention the difference between some great circle distances from your FMS and the values you would calculate. Might be due to which geodetic datum you are using versus your Boeing?

Is it possible that the airplane uses your planned altitude to compute the track length? You fly high enough that 2pi would be a small discrepancy against the charted .

The airplane FMC (Honeywell) doesn't care about altitude increasing the GC distance. I prove this to the inquisitive by plotting a 200 mm line at 90 degrees to the flight path; a 5,000 nm line and a 10,000 nm line also at 90 degrees to the flight. These three plots are all the same line of longitude but only coincide when directly over the shortest. The reason is that the shorter the line the closer to the surface of the earth it is, conversely, the longer the line the more it bisects the curve of the earth. Therefore they only coincide when at 90 degrees (vertically perpendicular) to the shortest. Otherwise it is a slant view.

The real reasons, a guess, I don't correct for an oblate spheroid (the earth); vendor error, how do they round and; there datum, airport central?, tower? Geographic centre? Nav aid fix? The error is extremely small in any case and I only use it as a gross check for fuel predictions at flight planning.

Cessna 170, what year? Nice and a tail dragged to boot. Lots of time on a 180 but it had floats!