As a must-have box for controlled airspace, Mode C transponders have been installed in just about every powered GA aircraft around.
In the coming years, many of them will have to be retired as changes to the radar system have overtaken the technology.
Upgrades around Melbourne and the Gold Coast have introduced the need for Mode S transponders, something the older cavity tube units can’t handle, prompting a need for aircraft owners to start looking for a newer solid-state model if they want to fly in CTA.
Airservice’s plan is to have Mode S radars also at Perth, Adelaide, Sydney, Cairns, Canberra and Brisbane by mid-2010.
Mode S (select) will bring several changes to the radar system, some of them visible, others not so.
For the pilot, it means that traffic information will be available from the radar feed if the aircraft has a Traffic Information System (TIS) installed.
Another advantage is that the aircraft identification will not be lost if the aircraft starts to squawk 7,700 (radio failure).
The other piece of trickery being added to transponders is the ADS-B capability.
Although Australia’s low-level ADS-B project is currently in the too-hard basket, the US manufacturers are building in the ability for the transponder to take information from the GPS unit and broadcast through an ADS-B Out squitter.
Aircraft in the vicinity fitted with ADS-B In units will know your every move.
So is it any value right now?
Only you can decide, but keep in mind that there are several modes of ADS-B.
There is no guarantee that if Australia implements ADS-B at low level the system will be compatible with the squitter built in to your transponder.
GARMIN
GTX 327
Garmin has given the old Mode A/C transponder a complete facelift with this model.
Instead of the traditional knob for On/Off/Standby/Alt, each function has its own button.
They have also opted for a push-button code selector and large VFR and ident buttons.
The display is yellow-on-black LCD.
There is also a built-in trip timer and pressure altitude indication.
WxHxL (mm): 159 x 42 x 222
Weight (kg): 1.4
TSO: C74c Class 1A
GTX 330
This is Garmin’s Mode S model and therefore the best of their range if you are looking to modernise your panel.
It has all the functions (and looks) of the GTX 327 but is also TIS capable.
Traffic information garnered by the Mode S can be displayed on any 400 or 500 series Garmin GPS.
WxHxL (mm): 159 x 42 x 282
Weight (kg): 1.9
TSO: C112
BENDIX KING
KT 76c
This is a Mode A/C unit with one big difference: the code is set by pushing buttons rather than twisting knobs, making code selection easier and faster.
For the thick-fingered among us there is also has a ‘clear’ button that wipes out code mistakes.
Gas plasma display makes it easy to read at night.
WxHxL (mm): 159 x 41 x 273
Weight (kg): 0.90
TSO: C74c Class 1A
TRIG
TT21
This is a completely unconventional unit, but has been designed for aircraft where weight and space are critical.
It has two parts: the controller and the transponder unit itself.
The controller is mounted in the panel in the same space as most round flight or engine instruments and is used to set the codes and work the functions.
The transponder can be mounted anywhere in the air frame.
This is a solid-state Mode S unit with ADS-B Out capability.
Code setting is done with only one knob, which may take some getting used to.
Worth a look if you have a recreational or LSA aircraft.
WxHxL (mm): Controller–45 x 45 x 64; Transponder–62 x 45 x 141
Weight (kg): 0.45
TSO: C112
MICROAIR
T2000SFL
Another good system to fit into tight panels.
This Australian-made unit is currently selling in 40 countries around the world and has GA approvals from all those that matter.
It is a basic unit that uses minimal knobs, but still has a VFR setting button.
The display can show you the code, pressure altitude and assigned altitude, with alerts when you break the limits.
It is only A/C, but at the time of writing Microair is believed to be well down the track with Mode S and ADS-B versions.
WxHxL (mm): 61 x 61 x 160
Weight (kg): 0.75
TSO: C74c Class 1A
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