Section 33.91 - Engine system and component tests(a) For those systems or components that cannot be adequately substantiated in accordance with endurance testing of § 33.87 , the applicant must conduct additional tests to demonstrate that the systems or components are able to perform the intended functions in all declared environmental and operating conditions.(b) Temperature limits must be established for those components that require temperature controlling provisions in the aircraft installation to assure satisfactory functioning, reliability, and durability.(c) Each unpressurized hydraulic fluid tank may not fail or leak when subjected to a maximum operating temperature and an internal pressure of 5 p.s.i., and each pressurized hydraulic fluid tank must meet the requirements of § 33.64 .(d) For an engine type certificated for use in supersonic aircraft, the systems, safety devices, and external components that may fail because of operation at maximum and minimum operating temperatures must be identified and tested at maximum and minimum operating temperatures and while temperature and other operating conditions are cycled between maximum and minimum operating values.Doc. No. 3025, 29 FR 7453, June 10, 1964, as amended by Amdt. 33-6, 39 FR 35469, Oct. 1, 1974; Amdt. 33-26, 73 FR 48285 , Aug. 19, 2008; Amdt. 33-27, 73 FR 55437 , Sept. 25, 2008; Amdt. 33-27, 73 FR 57235 , Oct. 2, 2008