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Cockpit Tutorial – Using the Trig Transponder

Using the trig transponder at AirBourne Aviation in Hampshire

Please note: There is a new checklist for the C42 now available that includes transponder steps. It is a legal requirement to use a transponder if one is fitted to the aircraft.

Understandably, some find radio procedures and the use of a transponder a daunting prospect, although few will readily admit it! However, it doesn’t have to be.

The transponder is an awesome bit of kit that can help you and help others around you stay safe in the air.

This article provides the procedures to use the transponder from start-up to in flight, to shutting down.

Where is the transponder?

The transponder is fitted, currently, to G-VI and G-YR. It is located in the centre console, at the bottom.

Location of the transponder in the C42

What do the dials and buttons do?

Here’s what the various buttons and dials do:

IDT – The ident button, used if requested to do so by air traffic control.

ENT – Enter key for making confirmations when you select the 4-digit numbers as you’re cycling them.

VFR – A very handy feature that resets the squawk to the inconspicuity code ‘7000’ without having to fiddle the knob to do so.

FN – The function button, it changes the functions available – no need to use this outside of configuring the unit.

Right knob – Adjusts the digits in the squawk part of the window.

Left knob – Cycles the various settings including ‘OFF’ (that one is obvious), ‘SBY’ meaning ‘stand-by’, ‘GND’ which is set for use on the ground, ‘ON’ and ‘ALT’ which then starts transmitting your altitude information as well as aircraft information.

TT21 Trig Transponder

Transponder use, example flight

Following the checklist, once the radio is on turn the transponder on using the left knob and rotate clockwise to ‘GND’.

Turn the transponder to GND

Once your pre-flight checks are complete, following the checklist, after setting the trim for take-off and checking flaps are as required, turn the left-hand knob all the way to “ALT”.

Turn the transponder onto ALT

You will now be in ‘Mode-S’ transmitting your position, aircraft information and altitude.

Once in the air and communicating with a LARS or similar air traffic service they will ask you to set a ‘squawk’.

To do this, turn the right-hand knob to get the first number. The Trig transponder will immediately start to change the first digit.

Turn the right knob to change the squawk code

Once the first digit is set, simply press the “ENT” button to move onto the next digit.

Press the ENT button to move to the next digit

Then use the right-hand knob again to change the digits.

Once you have established all four digits (double check to make sure you have the correct squawk code set), press the “ENT” button once more to then allow the Trig transponder to start transmitting the updated squawk code.

Once service with that LARS is complete they will likely ask you to “squawk 7000” and freecall your en-route station.

To reset the transponder to 7000, simply press the “VFR” button on the right-hand side.

VFR button to reset the transponder to 7000

(Please note, the above photos were done for illustration and therefore the setting for the left-hand knob in-flight will be “ALT” as previously described).

Once you are on the ground and clear of the active runway, following the checklist correctly, you must change from “ALT” status to “GND” status.

Turn the transponder to GND

With your shutdown checks being followed, turn off the transponder by turning the left-hand knob all the way anti-clockwise to the “OFF” position.

Questions and more information

The manual

The manual is available online here or you can find it in the AirBourne office – just ask a member of staff.

More questions to ask or need more help?

If you’re a student of AirBourne then please ask your instructor to go through the procedures with you.

If you’re an AirBourne member, then simply please ask us. We are more than happy to help and show you however many times you need. We all forget things from time to time. It’s far more shameful getting something wrong that could have easily been corrected than it is to ask one small question to avoid later problems.

Disclaimer: This article was written for information only and was up to date at the time of writing. Please always ask a qualified instructor for more information and a demonstration of proper operation before using.