Originally Posted by
uncle8
I am with you on this. The encoder is not required to be checked which makes me wonder if you really need a transponder check at all. ATC will tell you if your altitude transmission is incorrect just as they will tell you of any other transponder fault. Same as a VHF radio fault.
The encoder most certainly is required to be checked every 2 years. CAO 100.5 Appendix 1 Para 4.6 refers. It must be carried out in conjunction with the pressure altimeter check. This is the old AD/RAD/43.
The transponder test requirements are in CAO 100.5 Appendix 1 Para 14, this is the old AD/RAD/47 for non Part 42 aircraft, AD/RAD/47 still applies to Part 42 aircraft as the transponder tests weren't included in the Part 42 MOS.
As far as replacing a Mode C transponder - the key word is "installation".
Removing an unserviceable KT76A and replacing it with a serviceable or even brand new (if you could find one) KT76A is legal, you are not modifying the "installation" only replacing a component.
You can't pull out the KT76A and put in Narco Mode C.
This is covered in CAO 20.18 Para 9E - any aircraft built on or after 6 Feb 2014
or has it's transponder
installation replaced or modified after Feb 6 2014 - the installation being the whole system