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Page 4-6 GTX 330 Installation Manual
Revision G 190-00207-02
4.4.4 Altimeter Selection Priority
The installer must be aware of the GTX 330 priority for selecting encoded altimeter interconnections.
The GTX 330 searches in this sequence for altitude, and stops when it finds a valid pressure altitude
input.
Only approved devices may provide altitude to the GTX 330 in accordance with 14 CFR Part 91.217. In
addition, all altitude reporting devices installed in the aircraft must meet certification requirements of
14 CFR Part 91.413. The installer must select an altitude reporting device that is a certified altitude
source for the particular aircraft.
Altitude reporting equipment order of precedence:
1) ARINC 429 Air Data Computer (label 203, if configured W/ALT) (25’)
2) ARINC 429 EFIS (label 203, if configured W/ALT) (25’)
3) RS-232 data from CNX80/GNS 480 if so connected
4) RS-232 Fuel/Air Data Computer (if configured W/ALT.) (25’)
5) Shadin Altitude Serializer/Encoder (if configured for 25’)
6) Icarus Altitude Serializer/Encoder (if configured for 25’)
7) Parallel wire Gray Code input (100’)
8) Shadin Altitude Serializer/Encoder (if configured for 100’)
9) Icarus Altitude Serializer/Encoder (if configured for 100’)
It is the installing agency’s responsibility to determine that the installed encoder is compatible with the
selected altitude reporting criteria, either 100’ or 25’. Refer to Section 5.2.8 and 5.2.9 for the altitude data
reporting configuration.
4.5 Discrete Functions
4.5.1 Discrete Outputs
External suppression should be connected if another transponder or DME is installed in the aircraft
avionics system. The suppression pulses may not be compatible with all models of DME. In this case,
leave the suppression pin open. Known incompatible units are the Bendix/King KN 62, KN 64 and
KNS 80.
Table 4-6. Discrete Outputs Pin Assignments
Pin Name Pin Number I/O
ALTITUDE ALERT ANNUNCIATE* 19 Out
EXTERNAL SUPPRESSION I/O 31 In/Out
* This output is considered active if either the voltage to ground is < 1.9 V or the resistance to ground
is < 375 Ω. This output is considered inactive if the voltage to ground is 11-33 Vdc.