T-45C TS & ADV BIFP-09
steering mode, a TACAN course line, CDI or Planimetric, will also be displayed.
The T-45C display system is designed so that a TACAN channel may be tuned
anytime, and the TACAN kept in the ON position without causing a cockpit distraction.
When within range, the system will lock-on. If a properly tuned TACAN fails, the aural
identification tone will be lost. Unlike many analog systems, no TACAN warning flags
will appear on the HSI display.
If the bearing information fails after lock-on, the TACAN digital bearing readout, the
bearing pointer, and TACAN symbol will be removed. If the TACAN has only lost its
lock-on, the digital bearing readout and TACAN symbol will still disappear, but the
TACAN bearing pointer will rotate in a search mode. If a valid DME signal is lost or the
DME fails, all digital DME and the TACAN symbol will be removed until return of a valid
signal, and the CDI will go away.
(NOTE: For computation of digital TACAN time-to-go, the system uses whatever GS is
being computed at that precise moment on the existing aircraft heading. That resulting
GS will not necessarily be the same GS that would result after turning the aircraft to
proceed directly to the TACAN station. Depending on relative bearing of the TACAN
station and the actual wind direction/velocity, the GS and time-to-go computation may
be significantly different than those that are correct for a direct flight to the TACAN
The procedure for dealing with TACAN bearing/DME failure is:
1. Reset the desired channel.
2. Cycle the TACAN control panel to OFF and back to ON.
3. Check with ATC to determine if the subject TACAN is in operation, or select another
TACAN that is known to be in operation and within range.
4. Use VOR (if available), waypoints (non-IFR conditions), or request radar vectors.
ILS GLIDESLOPE FAILURE 188.8.131.52.9.2
The FWD/AFT selection made on the HSI MFD determines which NAV radio control
head is active. The frequency entered by the pilot will automatically direct the HSI MFD
to display an ILS or VOR legend.
Like VOR, ILS is only available and can only be selected in the HSI CDI mode. Once
ILS steering has been selected in the CDI mode, changing to HSI PLAN mode will
cause removal of the ILS course line and ILS CDI bar, but ILS steering needles will
continue to be displayed on both the HUD and ADI.