E6-B alt correction versus AIM 7-2-3 cold weather errors

[pbucko]

Consider:
E6-B does altitude correction, which corrects indicated altitude to true altitude, based on non-standard temperatures.

Also, AIM 7-2-3(d) refers to altimeter errors when the temperature is extremely cold, without regard to pressure altitude. (E6-B uses pressure altitude.)

Now:
Are these two items referring to the same errors, or are the two different types of errors?

If I'm 1000AGL over a 10,000' airport at -10C, the E6-B yields a correction of about 10' (makes sense, since I'm close to standard temp). The AIM TBL 7-2-3 indicates a correction of about 100' -- Why?

In both cases, there is zero error when I'm on the runway, because altimeter settings are "cooked" to make that true.
_________________
-Peter Buckner

 

[poadeleted20]

The referenced table is based on sea level airport elevation. Changes from that will change the table results. However, the text in that AIM section makes clear that the presentation is a "worst case" basis. If you have an E-6B handy, go with the computed data for the ambient conditions, as it will be more accurate. If you don't have one, use the AIM table as a "worst case" scenario -- the worst that happens is you miss an approach you could have made.

 

[pbucko]

Kinda... I mean close enough for flying, but...

Using standard formulas and a spreadsheet, I can build a table very similar to the one in AIM using sea level as the assumption, so thanks for that hint. There are a few numbers which are off. For example +10C 5000' above sea level airport results in 100' error rather than printed 90'. Odd, but the table may be using significantly more complicated calculations (wonder what...?)

But, does E6-B have errors for this kind of calculation?
Try calculating -20C at 5000' above sea level. Note the table refers to 'reported temperature' which we need to assume is station temp, not outside air temp. Convert using 1.98C per 1000 feet for -29.9 OAT.

Now, align Pressure altitude 5000' with -29.9C for altitude correction. Indicated 5000' converts to 4,350 or an cold weather error of 650, not 710 in the chart.

Does anyone have the 'real' calculation being done by the E6B for altitude correction?

I'm splitting hairs to better understand what all these calculations are, I readily admit the errors are generally minor.