In short, just like there are building codes for houses and buildings, Part 23 is the building code for current type-certificated Small Aircraft. For such an aircraft to continue to be legal and its Airworthiness Certificate to be valid, the aircraft must always meet the requirements of its building code, Part23. FAR Part 23 replaced the Civil Air Regulations, CAR 3, essentially back in 1958. However, the majority of requirements found in CAR 3 were transferred over into Part 23, granted with some major additions which will be discussed in this program. Part 23 describes and details all of the regulatory tests and processes that must be accomplished successfully in order to receive an aircraft Type Certificate from the FAA. When anyone desires to alter an aircraft, it is imperative that they determine the Certification Basis, such as CAR 3 or Part 23 for example.
It’s like replacing the furnace in a house previously built, let’s say about 25 years ago. If you can replace the furnace with one identical to the old one, you can continue to comply with the original building code. However, if such an identical furnace is no longer manufactured, and you need to install one that requires modification to the furnace cabinet, you will have to install it to comply with the current building code, probably much more expensively.