Gulfstream 100s, Astra SPXs and 1125 Westwinds are the latest business jet models to be the subject of an AD as a result of the FAA’s special certification review (SCR) of all pressurized airplanes after the October 1999 Payne Stewart Learjet 35 crash and several other incidents and accidents attributed to suspected oxygen deprivation. The proposed AD would require a revision to the jets’ flight manuals that would advise the crew to don oxygen masks immediately as the first step following a cabin altitude alert. The FAA said the flight manuals for these airplanes currently has the donning of oxygen masks as the second step.