A turbofan gas turbine engine comprises, in axial flow sequence, a heat exchanger module, a fan assembly, a compressor module, and a turbine module. The fan assembly comprises a plurality of fan blades defining a fan diameter (D). The heat exchanger module comprises a plurality of heat transfer elements.
The heat exchanger module is in fluid communication with the fan assembly by an inlet duct. The inlet duct has a fluid path length along a central axis of the inlet duct between a downstream-most face of the heat transfer elements and an upstream-most face of the fan assembly. The fluid path length is less than 10.0*D.