31 July 2011 C1 CIVIL AVIATION DEPARTMENT HONG KONG ...

CIVIL AVIATION DEPARTMENTHONG KONG, CHINAAirworthiness NoticeTHIS NOTICE GIVES DETAILS OF A MANDATORY ACTIONNo. 76Issue 330 September 2006ELECTRICAL POWER SUPPLIES FOR AIRCRAFT RADIO SYSTEMS1 Introduction1.1 Previous Issues of this Notice drew attention to the dangers of operation ofaircraft in which the entire radio installation was supplied via a singleelectrical feeder circuit, and stated that Certificates of Airworthiness wouldnot be issued or renewed in respect of aircraft certificated in the TransportCategory with such systems.1.2 Issue 2 of this Notice extended the applicability of the Notice to include allaircraft in any Category. Interpretative material has been added to giveguidance on the extent of the assessment to be made.2 RequirementThe electrical feeder arrangements shall be such that:(a)Where more than one radio system is installed, no likely single failure (e.g. afuse or a relay) will result in the loss of all radio systems.NOTE: It is strongly recommended that such a failure should only result in the loss of oneradio system.(b)Where duplicate radio systems, or radio systems which can duplicate afunction, are installed, no likely single failure (e.g. a fuse or a relay) will resultin the loss of both systems.3 Interpretation3.1 In examining electrical feeder arrangements to establish compliance withparagraph 2, the examination for likely single failures should include:(a)(b)the mechanical and electrical aspects of the supply circuit, includingthe return path of the electrical supply;the location within the electrical circuit of fuses, circuit breakers andAN-76 P.130 September 2006