Just a bit more about STC's

A supplemental type certificate (STC) is a type certificate (TC) issued when an applicant has received FAA approval to modify an aircraft 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.

Part of the process entails getting the manufacturers drawings of the aircraft itself. The faster they can be obtained the faster an engineer can do his thing. A good engineer can complete a project in two weeks. It is the magnetic field caused from the electronics of the part that is of concern. That magnetic field cannot interfere with other integral components. So two weeks to get the drawings, two weeks to complete the work by a good engineer and about a month for approval. Due diligence my good friends. I checked it myself. Getting the mechanical drawings from the manufacturer is usually the biggest delay. A good mechanical engineer plays a huge part. Once you get an STC for a particular make of aircraft the easier it gets to get another.

BL