The FAA is proposing to adopt a new airworthiness directive for all Dassault Falcon 50s. The proposed AD was prompted by a manufacturer revision to the airplane maintenance manual. The maintenance tasks and airworthiness limitations, as specified in the Falcon 50 AMM Chapter 5-40, have been identified as mandatory actions for continued airworthiness and include a corrosion-prevention and -control program and checking of overpressure tightness on pressurization control regulating valves. Failure to comply with AMM Chapter 5-40 at revision 21 might constitute an unsafe condition that could reduce the structural integrity of the airplane.