How does CDI scaling transition from terminal to approach sensitivity?
Beginning 2NM prior to reaching the final approach fix of an activated approach, the GPS will smoothly taper down the CDI scale from 1-NM full-scale deflection (from the center) to 0.3-NM at full-deflection over that 2-NM flight distance and reach a scale of 0.3-NM as the final approach fix is reached.
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&quot;When within 2 NM of the Final Approach Waypoint (FAWP) with the
approach mode armed, the approach mode will switch to active, which
results in RAIM and CDI changing to approach sensitivity. Beginning 2
NM prior to the FAWP, the full scale CDI sensitivity will smoothly
change from ±1 NM to ±0.3 NM at the FAWP. As sensitivity changes from
±1 NM to ±0.3 NM approaching the FAWP, with the CDI not centered, the
corresponding increase in CDI displacement may give the impression
that the aircraft is moving further away from the intended course even
though it is on an acceptable intercept heading. Referencing the
digital track displacement information (cross track error), if it is
available in the approach mode, may help the pilot remain position
oriented in this situation. Being established on the final approach
course prior to the beginning of the sensitivity change at 2 NM will
help prevent problems in interpreting the CDI display during ramp
down. Therefore, requesting or accepting vectors which will cause the
aircraft to intercept the final approach course within 2 NM of the
FAWP is not recommended.&quot;