Grandfather rights refer to a system that allows newer versions of an original aircraft design to be produced under the same Type Certificate. This process simplifies the approval needed compared to obtaining a brand-new Type Certificate. While certification standards have improved over time due to technological advancements and experience, these improvements do not always apply to similar aircraft made under variations of the original design. Notably, there is no set expiration for these grandfather rights, allowing them to last for many years. For example, the lineage of the Airbus A320 has extended to include models like the A321, A319, and A318. Similarly, the Douglas DC-9 evolved into the later MD-80 and MD-90 series, which eventually led to the Boeing 717.
