(2012) Service Advisory 1223 Rev A: Dual Transponder Operation

AFFECTED PRODUCTS

This advisory is applicable to all GTX 328 and GTX 330(D) transponders installed in dual-transponder configurations.

PURPOSE

Changing the squawk code or Flight ID on a transponder sends a change notification to Air Traffic Control (ATC), notifying them of the changed squawk code or Flight ID. This only occurs when the transponder is in an active mode (e.g. ON, ALT, or GND) and will not occur if the transponder is in STBY mode.

In dual-transponder installations, some operators have experienced difficulty with ATC resulting from setting a Flight ID or squawk code on the inactive transponder and then activating that transponder to change Flight ID or squawk code upon ATC request.

In dual-transponder installations, ATC does not always receive the change notification when a Flight ID or squawk code is changed on the inactive transponder and then set active.

PILOT ACTION

When instructed to change the squawk code, always change the squawk code on the active transponder.

When instructed to change the Flight ID, ensure the transponder is set to ON, ALT, or GND immediately following the Flight ID change.