A gas turbine engine comprising: a compressor section ; an air supply; an oil supply; and a fluid cooler comprising: an outer tube having an outer tube inlet at a first end of the fluid cooler and an outer tube outlet at a second end of the fluid cooler , a primary axis of the fluid cooler defined within the outer tube between the first end of the fluid cooler and the second end of the fluid cooler ; and a plurality of inner tubes extending within the outer tube between the first end of the fluid cooler and the second end of the fluid cooler , the plurality of inner tubes having a common inner tube inlet and a common inner tube outlet , the plurality of inner tubes extending helically about the primary axis of the fluid cooler , a first group of the plurality of inner tubes disposed at a first radius (R1) from the primary axis of the fluid cooler and a second group of the plurality of inner tubes disposed at a second radius (R2) from the primary axis of the fluid cooler , the second radius (R2) different from the first radius (R1), wherein the outer tube inlet is fluidly coupled to the oil supply. a compressor section ; an air supply; an oil supply; and a fluid cooler comprising: an outer tube having an outer tube inlet at a first end of the fluid cooler and an outer tube outlet at a second end of the fluid cooler , a primary axis of the fluid cooler defined within the outer tube between the first end of the fluid cooler and the second end of the fluid cooler ; and a plurality of inner tubes extending within the outer tube between the first end of the fluid cooler and the second end of the fluid cooler , the plurality of inner tubes having a common inner tube inlet and a common inner tube outlet , the plurality of inner tubes extending helically about the primary axis of the fluid cooler , a first group of the plurality of inner tubes disposed at a first radius (R1) from the primary axis of the fluid cooler and a second group of the plurality of inner tubes disposed at a second radius (R2) from the primary axis of the fluid cooler , the second radius (R2) different from the first radius (R1), wherein the outer tube inlet is fluidly coupled to the oil supply. an outer tube having an outer tube inlet at a first end of the fluid cooler and an outer tube outlet at a second end of the fluid cooler , a primary axis of the fluid cooler defined within the outer tube between the first end of the fluid cooler and the second end of the fluid cooler ; and a plurality of inner tubes extending within the outer tube between the first end of the fluid cooler and the second end of the fluid cooler , the plurality of inner tubes having a common inner tube inlet and a common inner tube outlet , the plurality of inner tubes extending helically about the primary axis of the fluid cooler , a first group of the plurality of inner tubes disposed at a first radius (R1) from the primary axis of the fluid cooler and a second group of the plurality of inner tubes disposed at a second radius (R2) from the primary axis of the fluid cooler , the second radius (R2) different from the first radius (R1), wherein the outer tube inlet is fluidly coupled to the oil supply. <EOS>