NOTE: NAV tuning is designed to enhance the VPU (VORTAC
Position Unit). The VPU will only use VOR/DME or DME only
navaids (includes TACAN and ILS) therefore, only VOR/DME or
DME only navaids will be displayed. In areas where a VOR only and
a DME only are on the same frequency and within line of sight of the
aircraft, entering the VOR identifier will result in the database replac-
ing the VOR identifier with the "usable" DME identifier. When this
occurs, the RANGE and BRG displays remain associated with the
VOR even though it is no longer displayed. This ambiguity will occur
when the frequency rather than the identifier is entered.
When the CDU keyboard is used to tune a navaid, the local VPU
database is searched for the tuned frequency. If found it is paired
with the nearest usable Navaid identifier associated with that fre-
quency. If the station identifier tuning method is used to tune the
radio. the identifier ultimately paired with the tuned frequency may
differ from the identifier originally entered. If the navaid is unusable,
that is, out of range, or a frequency conflict exists, dashes will be dis-
played in the IDENT field and the new frequency will be displayed.
Frequency - VERIFY that the ACTIVE frequency on the control
head and CDU displays agree.
If Station Frequency is Used:
TUNE Key -DEPRESS until NAV TUNE Page is displayed.
Line Select Key - DEPRESS to position cursor over desired
Frequency - INSERT or
VERIFY. (Figure 3-147)
NOTE: Trailing zeroes are
4. ENTER Key - DEPRESS.
5. Frequency - VERIFY that
control head display is
tuned to the desired fre-
Flight Management System