Heat exchanger for an aircraft

A gas turbine engine, comprising:

• a compressor;
• a combustor;
• a turbine;
• a heat exchanger in operative association with at least one of the compressor, the combustor, or the turbine, the heat exchanger comprising:
• an inlet plenum housing defining an inlet plenum configured to receive a fluid;
• an outlet plenum housing defining an outlet plenum configured to discharge the fluid from the heat exchanger;
• a core configured to heat or cool a first portion of the fluid, the core defining a plurality of fluid passages fluidly coupled to and extending from the inlet plenum to the outlet plenum;
• and
• a passive bypass defining a passive bypass flow path fluidly coupled to and extending between the inlet plenum and the outlet plenum, the passive bypass flow path being in parallel with at least a portion of the core such that a second portion of the fluid bypasses at least a portion of the core and flows continuously and unobstructed through the passive bypass flow path to the outlet plenum.