[. . . ] GTX 320 TRANSPONDER Pilot's Guide Operating The GTX 320 IDENT BUTTON REPLY LIGHT CODE SELECTION KNOBS FUNCTION SELECTION KNOB NOTES The GTX 320 owner accepts all responsibility for obtaining the proper license before using the transponder. The coverage you can expect from the GTX 320 is limited to "line of sight". [. . . ] The ALT position may be used in aircraft that are not equipped with the optional altitude digitizer, however, the only response will be discreet signals that do not contain altitude information. · TST--Turning the switch to the TST position tests the reply indicator. When released, it will automatically return to the ALT position. Any time the function switch is in the ON or ALT position the transponder becomes an active part of the beacon system. Select ON or ALT as late as practical prior to takeoff and switch to OFF or SBY as soon as practical after completing landing roll unless the change to SBY has been accomplished previously at the request of ATC. Code Selector The code selector consists of four, eight position switches that provide 4, 096 active identification codes. The selected code should be in accordance with instructions for IFR flight or rules applicable to transponder utilization for VFR flight. When making routine code changes, you should avoid inadvertent selection of codes 7500, 7600, or 7700 thereby causing momentary false alarms at automated ground facilities. For example when switching from code 2700 to code 7200, switch first to 2200 then 7200, NOT to 7700 and then 7200. This procedure applies to nondiscrete code 7500 and all discrete codes in the 7600 and 7700 series (i. e. , 7600-7677, 7700-7777) which trigger special indicators in automated facilities. An aircraft's transponder code (when available) is utilized to enhance the tracking capabilities of the ATC facility, therefore you should not turn the GTX 320 to SBY when making routine code changes. · 7500--Hijacking (Never assigned by ATC without prior notification of the pilot that his or her aircraft is subject to unlawful interference). · 7700--Emergency (All secondary surveillance radar sites are ready to receive this code at all times). [. . . ] Unit 5, The Quadrangle, Abbey Park Industrial Estate, Romsey, SO51 9AQ U. K. Telephone 011-44-1794-519944 FAX 011-44-1794-519222 Part Number 190-00133-00 Rev. [. . . ]