L2 Aviation issues supplemental type certificate (STC) which are a type certificate (TC) issued when an applicant has received FAA approval to modify an aeronautical product from its original design. The STC, which incorporates by reference the related TC, approves not only the modification but also how that modification affects the original design.
"We are absolutely happy with both L2's engineering and kits!!! I probably have said this before, but this has been one of the BETTER engineering/cert/kitting entities that we have had the experience of working with. You guys have been absolutely responsive with every request we have made (and even had strategically placed personnel available to come up to both our Install and Stores facility when the conditions warranted. Certainly above and beyond expectations. "