A failed HSI is caused by the GINA losing positional data (Figure 47). Without positional data, the DEU
doesnt display the VOR bearing or waypoints. TACAN digital bearing and range are displayed because
they are direct inputs to the DEU and dont require positional data from the GINA to be displayed.
Second is the LAW advisory. The possible implication for the pilot is that the aircraft is not positioned
where he thinks it is positioned. Such could result from a navigation error, or possibly a problem with a
navigation system. Immediately, take appropriate action to ensure aircraft safety. Then, determine why
the plane got into a LAW advisory circumstance. If the reason is not clear and acceptable, be certain to
cross-check and analyze all navigation and position information.
An advisory display can be removed by pressing the REJECT option displayed in the lower right-hand
corner of an MFD display (Figure 47). Only one advisory can be displayed at a time. If more than one is
applicable to the moment, the advisory with the highest priority will be displayed first. Pushing REJECT
will sequence the display to the next advisory notice. If no others are in sequence, the MFDs will be
cleared of all advisory windows.
TACAN Arcing with a Frozen HSI display compass rose
NOTE: At times when flying the T-45C, your instructor will want to use the simulate mode to alter the
MFD displays visible to you. Examples are when the instructor wants you to fly a no-gyro approach, or
some other scenario maneuver with a partial-panel display situation. In the real world, the DEU will stop
displaying data that it determines are invalid. If you have a heading problem, you can expect that the
MFD-displayed compass rose will disappear; however, in the simulate mode, the compass rose will
freeze, rather than disappear (Figure 49).
To arc, note the TACAN radial the plane is on. Make a 90-degree timed turn left or right (30 seconds at a
3-degree per second SRT bank angle). To determine heading, add 90 degrees for clockwise arc or radial;
minus 90 degrees to arc counterclockwise. To maintain the arc, hold the AOB that keeps the desired
TACAN DME range. On the HSI, watch for the tail of the TACAN bearing pointer to rise toward the top of
the compass rose. Appropriately lead your desired TACAN radial, performing a timed turn-to-inbound
REAL WORLD DISPLAY WITH
TRAINING PAGE DISPLAY WITH
FROZEN HSI DISPLAY SELECTED
Figure 49: TRAINING PAGE - FROZEN HSI