Abstract: A heat exchanger of a gas turbine engine includes a casing having a stepped incident-flow profile. An air volume flow is, in the region of the incident-flow profile, diverted such that a recirculation zone with a separation bubble forms in the flow. Downstream of the incident-flow profile, is a further stepped incident-flow profile. The flow is diverted such that, downstream of the further incident-flow profile, a further recirculation zone forms in which a separation bubble is present. In the region of the incident-flow profile and/or the further incident-flow profile, is an inlet of a flow duct which runs in the casing in the direction of a mouth. An air volume flow conducted through the flow duct emerges from the mouth at such an angle relative to the flow direction of the air volume flow that, downstream of the mouth, a recirculation zone with a separation bubble forms.