On 15-Aug-2003, (Snowbird) wrote:

Leave out the #2 OBS altogether and fill the hole with an electric
horizen gyro? We can identify intersections and back up the loc
with the GPS...course it's less precise...


If you fly "serious" IFR, that would definitely be my vote. The electric AI
will provide backup for failure of either the vacuum system or the primary
vacuum AI. Furthermore, the GPS will identify location of an intersection
with far GREATER accuracy than a pair of VOR receivers/CDIs, or even a
VOR/CDI and a DME. Think about it: if the CDI has an error of only 1
degree, at 40 nm from the VOR station that translates to a lateral error of
about .7 nm. By comparison, the GPS is accurate laterally to a matter of a
few meters.

You are correct that this setup will not provide localizer backup in the far
less likely event of failure of the #1 Nav or its CDI, but you still have
the approach-approved GPS for that situation

-Elliott Drucker