ELT batteries shall be replaced at the interval recommended by the ELT manufacturer.
Altimetry Devices - Altimeters and other Altimetry devices installed in aircraft operating under Instrument Flight Rules, or under visual flight rules in Class B Airspace shall be calibrated at intervals not exceeding 24 months, to the standard outlined in Appendix B of Chapter 571 of the Airworthiness Manual.
For the purpose of this section, the term "other altimetry devices" includes any air data computer, or other barometric device, providing a flight crew station, or an auto pilot, or automatic pressure altitude reporting system with altitude data derived from static pressure.
Air Traffic Control (ATC) Transponders - ATC Transponders, including any associated altitude sensing reporting mechanisms, where installed, shall be tested every 24 months, in accordance with Appendix F of Chapter 571 of the Airworthiness Manual.
CAR 625 Appendix C has lots of useful information in it that will help keep your certified aircraft legal and hopefully safer, too.
Modifying your aircraft
Certified aircraft can be modified, it just takes more paperwork than some other categories of aircraft!
One of the key things to remember is that, other than “standard parts” (like AN bolts that are made to Mil Specs), pretty much everything that you permanently attach to an aircraft has to be a certified part. Not only the part itself has to be approved, but the way it is installed requires approval, too. This keeps the aircraft’s certified status intact and ensures that any modifications have been well engineered and flight-tested to ensure that they don’t reduce the safety of the aircraft or imperil its occupants.
In Canada there are basically two legal ways to modify a certified aircraft:
Supplementary Type Certificates (STCs)
Limited Supplementary Type Certificates (LSTCs)
The USA has a third method called a “field approval” or FAA 337 procedure that allows “one-off” approvals to be made in the field by an inspector, but these do not exist in Canada, nor do we have an equivalent.
If you really have your heart set on modifying an aircraft greatly and the STCs do not exist to do the modifications that you want to do, then it is going to be difficult to get approvals for the work. Consider that a certified aircraft may not be the right aircraft for
COPA Guide to Certified Aircraft 40