User's Manual

TT21 Transponder Installation Manual 19 January 2009
00560-00 Issue AA
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replies for 18 seconds. IDT will appear in the display.
FN Pressing the FN button provides access to changing the Flight
ID.
VFR Pressing the VFR button sets the transponder to the pre-
programmed conspicuity code. Pressing the button again
restores the previous squawk code.
ENT The ENT button enters a digit in the code selector.
8.5 Code Selector Knob
The right hand knob is used to set squawk codes and the Flight ID. The FN button selects which will
be updated. Turning the knob will highlight the first digit on the display, and the digit can be changed
as required. Press the ENT button to advance to the next digit. When ENT is pressed on the last digit,
the new squawk code or Flight ID will replace the previous value. If the code entry is not completed
within 7 seconds, the changes are ignored and the previous code restored.
1200 VFR code in the USA
7000 VFR code commonly used in Europe.
7500 Hijack code
7600 Loss of communications
7700 Emergency code
The Flight ID should correspond to the aircraft call sign entered on your flight plan. If no flight plan is
active, the aircraft registration should be used as your Flight ID. Use only letters and digits. If the
Flight ID is less than 8 characters long, entering a blank character will end it.
8.6 Altitude Encoder Warm Up
The built in altitude encoder uses a sensor that is temperature dependent. A small internal heater
circuit keeps the sensor at the correct temperature. When the ambient temperature is below 0°C there
may be a delay between switching on the transponder and seeing an altitude reported. In very cold
weather this delay can be up to 5 minutes. You should always switch on the transponder (usually to
GND mode) before taxiing to the runway, to ensure that the sensor is operating before you become
airborne.
8.7 General Low Temperature Operation
The TT21 is certified to operate correctly down to -20°C, but at low temperatures the display may be
impaired. On a cold day you may need to wait for the cockpit to warm up to ensure normal operation.
8.8 Warning Messages
If the transponder detects a problem, the screen will indicate WARNING and a brief statement of the
problem. Depending on the nature of the problem, your transponder may not be replying to
interrogations. Note the message on the screen and pass that information to your avionics maintenance
organisation. Press ENT to clear the message; if the fault is still present the message will reappear.
8.9 Fault Annunciation
If the transponder detects a catastrophic internal failure, the screen will indicate FAULT and a brief
statement of the problem. No replies will be made to interrogations when a fault has been detected.
Some FAULT indications can be recovered by switching the transponder off and back on again,
although in all cases a FAULT code implies that there is a fault with the transponder or the installation.
Page 22 Trig Avionics Limited