New Cold Weather Corrections
I'm looking at the new cold temperature correction chart for approach plates (latest AIP update, RAC 9-11).
In the example, when the corrected altitude is 3611.4', for the FAF, they say to fly 3700', but when it is 3013.4, for the MDA, they say to fly 3000'. Unexplained inconsistency.
Also, their method of calculation seems a little cockeyed. It looks like they've arbitrarily chosen the 2000' and 1500' errors to subtract, when they could have just read the 500' error off the chart. Then they use that to calculate an error per foot of 0.3 - ONE significant figure which they then multiply out to produce a result of 521.4 FOUR significant figures, and a implied level of precision inappropriate to aircraft altimeters.
The way I usually do the calculation is:
aerodrome elevation 2262'
aerodrome temperature -50 degrees
MDA straight in 2840'
2840-2262=578
500' corresponds to a 150' correction
780' ~=800' - 240' correction, so 24' for 78'
150' + 24' = 174'
2840 + 174 = 3014' which I'd round up to the nearest thing I could fly, 3020'.
Comments?