A gas turbine engine comprising a system for cooling air, the system comprising: a bypass airflow channel existing outside of an engine core; a chamber comprised inside the engine core comprising: a chamber outboard surface (312; 412); and a chamber interior (308; 408); and a heat exchanger (320; 420) coupled to the chamber outboard surface (312; 412), the heat exchanger (320; 420), comprising: a heat exchanger base; and a cooling tube (321; 421) comprising a tube entrance end (322; 422) coupled to the heat exchanger base, a tube exit end (326; 426) coupled to the heat exchanger base, and a tube body between the tube entrance end (322; 422) and the tube exit end (326; 426) disposed inside the chamber interior (308; 408), the tube body encompassing a tube interior, wherein the tube interior is in fluid communication with the bypass airflow channel; wherein the chamber further comprises a chamber side surface (313; 413) coupled to the chamber outboard surface (312; 412), characterised in that: the chamber side surface (313; 413) comprises a side surface inlet (315; 415) that is configured to place a hot secondary airflow (336; 436) in physical contact with the cooling tube (321; 421), the heat exchanger (320; 420) is configured to cool the hot secondary airflow (336; 436) in the chamber to produce a cooled secondary airflow (338; 339; 438); the chamber further comprises a chamber exit surface (314; 414) coupled to at least one of the chamber outboard surface (312; 412) or the chamber side surface (313; 413), and the chamber exit surface (314; 414) comprises an exit hole configured to allow the cooled secondary airflow (338; 339; 438) out of the chamber interior (308; 408). a bypass airflow channel existing outside of an engine core; a chamber comprised inside the engine core comprising: a chamber outboard surface (312; 412); and a chamber interior (308; 408); and a chamber outboard surface (312; 412); and a chamber interior (308; 408); and a heat exchanger (320; 420) coupled to the chamber outboard surface (312; 412), the heat exchanger (320; 420), comprising: a heat exchanger base; and a cooling tube (321; 421) comprising a tube entrance end (322; 422) coupled to the heat exchanger base, a tube exit end (326; 426) coupled to the heat exchanger base, and a tube body between the tube entrance end (322; 422) and the tube exit end (326; 426) disposed inside the chamber interior (308; 408), the tube body encompassing a tube interior, wherein the tube interior is in fluid communication with the bypass airflow channel; a heat exchanger base; and a cooling tube (321; 421) comprising a tube entrance end (322; 422) coupled to the heat exchanger base, a tube exit end (326; 426) coupled to the heat exchanger base, and a tube body between the tube entrance end (322; 422) and the tube exit end (326; 426) disposed inside the chamber interior (308; 408), the tube body encompassing a tube interior, wherein the tube interior is in fluid communication with the bypass airflow channel; wherein the chamber further comprises a chamber side surface (313; 413) coupled to the chamber outboard surface (312; 412), characterised in that: the chamber side surface (313; 413) comprises a side surface inlet (315; 415) that is configured to place a hot secondary airflow (336; 436) in physical contact with the cooling tube (321; 421), the heat exchanger (320; 420) is configured to cool the hot secondary airflow (336; 436) in the chamber to produce a cooled secondary airflow (338; 339; 438); the chamber further comprises a chamber exit surface (314; 414) coupled to at least one of the chamber outboard surface (312; 412) or the chamber side surface (313; 413), and the chamber exit surface (314; 414) comprises an exit hole configured to allow the cooled secondary airflow (338; 339; 438) out of the chamber interior (308; 408).