you – perhaps putting the aircraft in the Owner Maintenance category or buying an amateur-built or basic ultralight aircraft would be a better choice, as modifications by the owner are permitted in those categories. The COPA Guides to Amateur Builts and Ultralights provide more information on those categories of aircraft.
A Supplementary Type Certificate (STC) is the paperwork that is issued to indicate that a modification is approved for an aircraft. It can be approved for a range of serial numbers or all aircraft of one type.
When you buy a modification kit for your aircraft (it could be a door latch, camera window, float installation, almost anything) it will come with:
STC paperwork that shows that the modifications is approved for your aircraft
(usually with a range of serial numbers)
Installation instructions for the modification
Flight Manual or POH supplements that show how the aircraft performance
changes (if at all)
Instructions for Continuing Airworthiness (ICAs) to show you how to maintain the aircraft with this modification installed. After the kit is installed and your AME has signed off the entry in the Technical
Record showing that the modification is complete, ensure that you put the complete paperwork into the Technical Record (can be a file folder) so that there is a permanent record of the mod. Add any STC supplements to the POH, if required. Next ensure that you make whatever changes are required to your Maintenance Schedule to reflect the extra requirement of the STC installation – if any!
One complaint aircraft owners often make about STCs are that they can be expensive. The most obvious cases of this effect are “auto fuel” STCs where the mod kit only provides placards, stickers and STC paperwork – no actual parts at all! Typically these still cost several hundred dollars – quite a lot of money for a few stickers! The answer is that you are paying for the benefits of an extensive engineering assessment and flight test program that proved that the mod worked and is safe. The aircraft’s certification is intact even after the mod is incorporated and you pay for that when you order the mod kit!
You can get a complete list of available STCs for your aircraft if it was certified in the USA on the FAA website.
COPA Guide to Certified Aircraft 41