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Add an altitude encoder to allow Mode A to Mode C upgrade in a certified aircraft

I know that any new transponder that you fit has to be Mode S. But I have an aircraft that has to be ferried from the UK to Bulgaria and it has a mode A transponder fitted. For reasons out of my control no one is keen to upgrade the transponder to mode S. But the transponder that’s fitted is capable of working as a mode C unit I was therefore wondering if its possible to simply add an altitude encoder.

If needed I’ve no problems getting across France and through Germany with a Mode A only. Does anyone know the situation with

Austria, Hungary, Romania, Bulgaria

or

Czech republic, Slovakia, Hungary, Romania, Bulgaria?

It will be flown VFR

That’s a very good Q. IMHO the answer is Yes. The transponder itself is not being changed, after all.

Actually an altitude encoder may have been fitted at some point in the past. Today, there should be almost no genuine Mode A installations left. And, in the new UK climate, a lot of people (incuding flying schools) are allowing altitude encoders on Mode C units to remain broken, and maybe some have removed them to create a Mode A installation. So you would not be “modifying” anything; just repairing it.

Administrator
Shoreham EGKA, United Kingdom

AIP Austria
AIP Hungary
AIP Romania

Neither of these mention a transponder as a mandatory equipment. You have to operate it if you carry one though, but that´s what SERA says too. In Romania you need one flying in controlled airspace, but most of the country seems to be Class G below FL105, excluding the TMAs.

The Bulgarian AIP can only be seen online after registration, but you can download it in Skydemon. You´ll need a transponder there flying through airspace C and TMZs.

You should be good to go without modification.

EDFE, EDFZ, KMYF, Germany

Super. Thank you

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