Heat exchanger for an aircraft, the heat exchanger arranged along a longitudinal direction X-X' and comprising: - a casing defining an inner chamber and comprising an inlet, an outlet, a first (11.1) and second (11.2) lateral walls opposite each other and extending between the inlet and the outlet and an upper and a bottom wall; the casing being configured to be in fluid communication with a source of incident flow of coolant through the inlet so that in an operative mode of the heat exchanger a flow of coolant flows through the inner chamber from the inlet to the outlet following the longitudinal direction X-X'; - a plurality of plates housed in the inner chamber of the casing extending substantially parallel to the longitudinal direction X-X', each of the plurality of plates being spaced from each other between the first lateral wall (11.1) and the second lateral wall (11.2) along a transverse direction Y-Y' perpendicular to the longitudinal direction X-X' from one of the lateral walls (11.1, 11.2) to the other lateral wall (11.1, 11.2) of the casing; and - a plurality of channels defined between contiguous plates; wherein each of the plurality of plates comprises a leading edge oriented towards the inlet and configured for diverting the incident flow of coolant towards the contiguous channels; at least a plurality of the plates comprises an inner hollow area extended in a direction perpendicular to both longitudinal direction X-X' and transverse direction Y-Y' and configured to be connected to a source of hot bleed air; the leading edges of a first group (14.1) of plates are arranged according to a stepped pattern, such that each leading edge is arranged in a downstream position according to the longitudinal direction X-X' with respect to the inlet and to the leading edge of a contiguous plate; the heat exchanger further comprises a first gap defined between the first group (14.1) of plates and the first lateral wall (11.1) of the casing, so that the first gap allows to stablish a fluid communication of coolant through the first group (14.1) of plates between the inlet and the outlet of the casing; and the distance between each leading edge of the first group (14.1) of plates and the first lateral wall (11.1) according to the transverse direction Y-Y' decreases along the longitudinal direction X-X'. - a casing defining an inner chamber and comprising an inlet, an outlet, a first (11.1) and second (11.2) lateral walls opposite each other and extending between the inlet and the outlet and an upper and a bottom wall; the casing being configured to be in fluid communication with a source of incident flow of coolant through the inlet so that in an operative mode of the heat exchanger a flow of coolant flows through the inner chamber from the inlet to the outlet following the longitudinal direction X-X'; - a plurality of plates housed in the inner chamber of the casing extending substantially parallel to the longitudinal direction X-X', each of the plurality of plates being spaced from each other between the first lateral wall (11.1) and the second lateral wall (11.2) along a transverse direction Y-Y' perpendicular to the longitudinal direction X-X' from one of the lateral walls (11.1, 11.2) to the other lateral wall (11.1, 11.2) of the casing; and - a plurality of channels defined between contiguous plates; each of the plurality of plates comprises a leading edge oriented towards the inlet and configured for diverting the incident flow of coolant towards the contiguous channels; at least a plurality of the plates comprises an inner hollow area extended in a direction perpendicular to both longitudinal direction X-X' and transverse direction Y-Y' and configured to be connected to a source of hot bleed air; the leading edges of a first group (14.1) of plates are arranged according to a stepped pattern, such that each leading edge is arranged in a downstream position according to the longitudinal direction X-X' with respect to the inlet and to the leading edge of a contiguous plate; the heat exchanger further comprises a first gap defined between the first group (14.1) of plates and the first lateral wall (11.1) of the casing, so that the first gap allows to stablish a fluid communication of coolant through the first group (14.1) of plates between the inlet and the outlet of the casing; and the distance between each leading edge of the first group (14.1) of plates and the first lateral wall (11.1) according to the transverse direction Y-Y' decreases along the longitudinal direction X-X'.