1. An aircraft, comprising: an aircraft cabin adapted to be pressurized; a gas turbine engine, wherein the gas turbine engine includes at least one engine bleed; an environmental control system (ECS) operable to receive bleed air from the at least one engine bleed and to provide conditioned air to the aircraft cabin, the ECS including: a heat exchanger operable to remove heat from an airflow therethrough; first sensors operable to detect environmental operating conditions of the heat exchanger; second sensors operable to detect airflow conditions in the heat exchanger; a controller operable to: receive environmental operating conditions data for the heat exchanger from the first sensors; receive measured values from sensors measuring parameters of the heat exchanger from the second sensors; retrieve from a first data structure an operating model for the heat exchanger based on the received environmental operating conditions, wherein the retrieved operating model includes estimated values for the sensors; calculate differences between the estimated values and the measured values; compare the calculated differences to at least one threshold value; upon the differences exceeding the at least one threshold value: compare the calculated differences to abnormal operation models in an abnormal operation library data structure; and upon the calculated differences matching an abnormal operation model in the abnormal operation library data structure, output an abnormal operation identity associated with the matched abnormal operation model.