Text in force at 29-59: from 29-26, effective 3 Oct 1988.
[For cooling fans that are a part of a powerplant installation the following apply:
(a) Category A. For cooling fans installed in Category A rotorcraft, it must be shown that a fan blade failure will not prevent continued safe flight either because of damage caused by the failed blade or loss of cooling air.]
(b) Category B. For cooling fans installed in category B rotorcraft, there must be means to protect the rotorcraft and allow a safe landing if a fan blade fails. It must be shown that--
(1) The fan blade would be contained in the case of a failure;
(2) Each fan is located so that a fan blade failure will not jeopardize safety; or
(3) Each fan blade can withstand an ultimate load of 1.5 times the centrifugal force expected in service, limited by either--
(i) The highest rotational speeds achievable under uncontrolled conditions; or
(ii) An overspeed limiting device.
[(c) Fatigue evaluation. Unless a fatigue evaluation under Sec. 29.571 is conducted, it must be shown that cooling fan blades are not operating at resonant conditions within the operating limits of the rotorcraft.]
53 FR 34215 · Source