Arcing procedures will only be encountered with overlay approaches but it must be noted that
DME arcing procedures flown with the GPS are significantly different than traditional
VOR/TACAN arcing approaches. DME arcing approaches are flown in the LEG mode.
Selecting an approach with an arc segment will result in IAF's 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 and 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 arcing approaches
until the aircraft is closer to the destination. Once the arc is selected, the SUPER NAV 5 page can
be used to display it.
Once established on the arc, the CDI will display left/right guidance relative to the curved arc.
Note 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 SUPER
NAV 5 page. This is important to note if there are any step down 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.
Select cockpit navigation source to GPS.
Tune and ID all available ground based NAVAIDS for back up.
7-44 INSTRUMENT NAVIGATION