ESDU 94040 discusses how the maximum cabin pressure differential and the rate of change of cabin pressure affect rates of climb and descent, particularly of civil aircraft. The cabin pressure differential is governed by the capability of the air-conditioning system, the strength of the fuselage and the maximum operating altitude of the aircraft. A sketch illustrates how cabin pressure and pressure differential affect operating altitude and indicates where aircraft of various classes operate. Excessive rate of change of pressure can build up a differential pressure across the eardrums and at 0.5 lbf/sq in (3.45 kN/sq m) would cause pain. For civil aircraft restricting the rate of change of cabin pressure is a major factor in determining descent profile and has also to be considered in climb although to a lesser extent. A further sketch illustrates possible climb and descent profiles chosen to maintain cabin pressure and its rate of change within the necessary restrictions while not exceeding cabin differential pressure limits.