05-22-2018, 04:25 PM
NTSB suggests changes in airplanes and/or procedures now and again. the FAA makes the changes happen (called Airworthiness Directives or ADs). They're compulsory. Some within a time or cycle frame, occasionally 'before next flight' which makes the aircraft unairworthy until the AD has been complied with. Not all NTSB recommendations end up being compulsory.