The term "grandfathered" is used in FAA literature for both pre-date (literally) and the designed before a regulation came into being.
The reason it exists is otherwise the FAA could release a new requirement that would halt a pre-existing production line that didn't meet it.
> Because part 135 operators will have limited ETOPS operations, the FAA has decided to grandfather from today's rule all part 135 airplanes manufactured up to 8 years from the effective date of the rule. For purposes of airworthiness requirements, part 135 operators may use these airplanes in ETOPS without certification under § 25.1535. This is a change from the NPRM, which proposed grandfathering only those airplanes that were on an operator's operations specifications up to 8 years after the rule. Under the NPRM, they would then have had to remain on the operator's operations specifications to continue to operate ETOPS.
> b. This Advisory Circular (AC) provides guidance to affected U.S. operators that operate aircraft outside the United States with aircraft that were never required to be noise certified. If you have such an aircraft, this AC outlines the noise certification requirement dates so you can confirm that your aircraft indeed pre-dates the requirements and should be considered acceptable. We use the term “grandfathered” for these aircraft. We strongly recommend operators of such aircraft to use the FAA form in Appendix 1 that includes a grandfather clause.
> These seats should provide adequate vision to the pilot's panel and forward windows in visual system models. "Grandfather rights" prevail on previously approved simulators; however, efforts should be made to improve surveillance visibility. These observer seats need not represent the aircraft seats.
The reason it exists is otherwise the FAA could release a new requirement that would halt a pre-existing production line that didn't meet it.
> Because part 135 operators will have limited ETOPS operations, the FAA has decided to grandfather from today's rule all part 135 airplanes manufactured up to 8 years from the effective date of the rule. For purposes of airworthiness requirements, part 135 operators may use these airplanes in ETOPS without certification under § 25.1535. This is a change from the NPRM, which proposed grandfathering only those airplanes that were on an operator's operations specifications up to 8 years after the rule. Under the NPRM, they would then have had to remain on the operator's operations specifications to continue to operate ETOPS.
https://www.federalregister.gov/documents/2007/01/16/07-39/e...
> b. This Advisory Circular (AC) provides guidance to affected U.S. operators that operate aircraft outside the United States with aircraft that were never required to be noise certified. If you have such an aircraft, this AC outlines the noise certification requirement dates so you can confirm that your aircraft indeed pre-dates the requirements and should be considered acceptable. We use the term “grandfathered” for these aircraft. We strongly recommend operators of such aircraft to use the FAA form in Appendix 1 that includes a grandfather clause.
https://www.faa.gov/regulations_policies/advisory_circulars/...
> These seats should provide adequate vision to the pilot's panel and forward windows in visual system models. "Grandfather rights" prevail on previously approved simulators; however, efforts should be made to improve surveillance visibility. These observer seats need not represent the aircraft seats.
https://www.faa.gov/documentLibrary/media/Advisory_Circular/...
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