Why is the alert for Density Altitude based on AGL instead of MSL?
This is because we feel the user would want to know about density altitudes that are above and beyond the field elevation. There’s little point in warning an Aspen, CO pilot about density altitude in excess of 3500 MSL since they would already expect that, but a pilot on the eastern seaboard would certainly want to know that. Therefore using AGL instead of MSL provides the user with more pertinent alerts as they change from airport to airport.
