Abstract: A gas turbine engine comprises a centrifugal compressor (4), an air diffuser (8), a heat exchanger (10), combustion apparatus (12), and first and second turbines (14,18). The combustion chamber assembly (22) comprises a primary, a secondary and a tertiary fuel and air mixing ducts (54,78,98). The compressor (4), diffuser (8), primary and secondary fuel and air mixing ducts (54,78) and turbines (14,18) all comprise means (6,8,16,20) for varying the mass flow area at their inlets such that in operation the amount of air mass through each component may be independently variable. Under part power conditions the mass flow is reduced and under full power conditions the mass flow is increased thereby maintaining a substantially constant gas cycle throughout the engine.