I am confused regarding the final route segment LSALT for calculating alternate minima for destination with no aids for an IFR day flight: AIP ENR 1.1 para 11.7.3.2.
Let's assume a published route's LSALT is 3600ft, but the Grid LSALT for the destination is 2000ft, which do altitude should I use?
What about the other way around? Route LSALT = 2000 and Grid LSALT = 3600ft?
Does the same rule apply to LSALT calculated i.a.w. AIP GEN 3.3 para 4?
Thanks 😀
Excellent question.
I think it largely depends on the aircraft’s navigation system. If the aircraft is capable of operating to RNP 2 specs (GPS as primary navigation sensor), we can plan using the LSALT of the published route shown on ERC or TAC.
Otherwise, or if there is no published route, we must either
a) use Grid LSALT or
b) use a WAC to calculate the lowest safe tolerance area on either side of the intended track as described in GEN 3.3 4.6
Assuming we agree on this, is this another version of your question:
“If I had the latest GPS and can plan to use the published route LSALT, why coudn’t I plan using the Grid LSALT (or the tolerance area) if that figure is lower?”
If so, I would like to know too.
: )
