FROM THE TIMES The sudden loss of pressure in an airliner cabin as occurred on the Ryanair flight is a frightening and potentially painful experience for passengers but it is does not usually endanger the aircraft Half a dozen episodes of rapid pressure loss have been suffered by airliners over the past year Pilots follow a standard procedure if the cabin pressure suddenly drops while at cruising altitude They don the oxygen masks which are constantly at their shoulder and put the aircraft into an emergency descent to about 8 000 ft above sea level the altitude at which the air becomes comfortably breathable At the same time the crew would have declared an emergency to the en route air traffic control and requested immediate clearance to the lower altitude and landing at a nearby airport In the meantime the oxygen masks will have deployed automatically to supply passengers and other crew during the descent The Ryanair Boeing 737 performed exactly this procedure after it suffered pressure loss The pilots descended from about 35 000 ft to 8 000 ft in five minutes according to the authorities at Limoges airport where it landed The media and passengers may call such manoeuvres a plunge or a free fall but the descent rate of about 5 600 ft per minute is perfectly controlled and within the normal performance of the aircraft assuming that all its flight systems are functioning