T-6A INSTRUMENT NAVIGATION
with an arc segment will result in IAFs being displayed that are not intuitively obvious. An
example is the IAF D220L. In this case, the D stands for DME arc, 220 is the radial the
waypoint lies on, and L indicates the distance of the arc. L is the 12th letter of the alphabet and
indicates a 12 DME arc. Once an IAF is selected for an arcing approach, the GPS determines
which radial of the reference VOR the aircraft is presently located on. A waypoint is created that
is located at the intersection of the present radial and the DME arc. This waypoint is then loaded
into the approach with the nomenclature described above. The GPS does not, however, take into
account the geometry of the active flight plan when determining the arc intercept point. This
point is defined solely on the present radial and the defined arc distance from the reference
NAVAID. For this reason, it is better to delay selecting DME arc approaches until the aircraft is
closer to the destination. Once the arc is selected, the SuperNAV 5 page can be used to display
Once established on the arc, the CDI will display left/right guidance relative to the curved arc.
Note also the distance to the active waypoint is the distance from the present position to the
active waypoint, not the distance along the arc. The GPS displays ARC XXX (the XXX will be
the radial from the reference NAVAID the aircraft is presently on) in the bottom line of the
SuperNAV 5 page. This is important to note if there are any stepdown altitudes on the arc
defined by a radial passage. Once established on a final course to the FAF, the approach
procedures remain the same as in RVFAC.
If the aircraft is on the arc, the CDI will be centered. The GPS
needle will point to the next WPT not the NAVAID. Use the CDI
to stay on the arc.
GPS ARCING APPROACH
Select and load desired approach into the active flight plan. (APT 8 page, right side)
The GPS will pick the closest point on the arc to intercept, which
may not be the IAF the pilot selects. Look at the active WPT.
Tune and ID all available ground base NAVAIDs for backup.
3. Brief the Approach. If required, determine stepdown altitudes using the profile view on the
8-12 GLOBAL POSITIONING SYSTEM