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 § 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.Amdt. 29-13, 42 FR 15046, Mar. 17, 1977, as amended by Amdt. 29-26, 53 FR 34215, Sept. 2, 1988 Secs. 313(a), 601, and 603, 72 Stat. 752, 775, 49 U.S.C. 1354(a) , 1421 , and 1423 ; sec. 6(c) , 49 U.S.C. 1655(c)