Garmin GNC 420A Installation Manual page 99

5.3.4 Deviation & Flags Check
5.3.4.1 Analog Deviation & Flags
The analog deviation (LEFT/RIGHT and UP/DOWN), TO/FROM, and FLAG (lateral and vertical) outputs
to a CDI or HSI should be verified in flight with potential sources of electrical noise such as autopilot,
flaps, gear, heater blowers, etc. operating. Lateral deviation and flags may be checked with either GPS or
VOR/ILS, and vertical deviation and flags must be checked with Glideslope. Verify that the flags are
hidden at the correct times, and that the flag is in view at the correct times.
5.3.4.2 EHSI Deviation Scaling (Only if HSI/CDI is driven by the 400 Series unit via serial data)
With the 400 Series unit locked onto a GPS fix, activate an OBS waypoint about 20 nautical miles from the
present position.
1. With 5.0 nautical mile CDI sensitivity, adjust the OBS course for approximately half-scale
deflection on the 400 Series unit's Default Navigation page. Verify that the EHSI displays a
similar half-scale deviation.
2. Repeat step 1 with 1.0 nautical mile CDI sensitivity. The CDI sensitivity may be manually set on
the AUX SETUP page, using the "CDI / ALARMS" menu item.
3. Repeat step 1 with 0.3 nautical mile CDI sensitivity.
5.3.5 Crossfill Check (Only if dual units installed with RS-232 crossfill connected)
Turn on both 400 Series units in the aircraft. For each 400 Series unit:
1. Select the first AUX page (titled "FLIGHT PLANNING").
2. Select "CROSSFILL".
3. Verify that the displayed status is "Ready". If "Not Available" is displayed, there may be an RS-
232 wiring problem between the two 400 Series units.
5.3.6 VHF COM Interference Check (GNC 420 and GNS 430 Only)
Once the Signal Acquisition Test has been completed successfully, perform the following steps:
1. View the Satellite Status Page and verify that 7 to 8 satellites have been acquired.
2. Verify that the GPS "NAV" flag is out of view.
3. Select 121.150 MHz on the 400 Series COM transceiver.
4. Transmit for a period of 20 seconds.
5. Verify that the GPS "NAV" flag does not come into view.
6. Repeat steps 4 and 5 for the following frequencies:
•
121.175 MHz
•
121.200 MHz
•
131.250 MHz
•
131.275 MHz
•
131.300 MHz
7. Repeat steps 3 through 6 for all COM transceivers installed in the aircraft.
8. If the GPS "NAV" flag comes into view, refer to Section 2.2.7 for options to improve performance.
400 SERIES INSTALLATION MANUAL
P/N 190-00140-02
Page 5-17
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