FAR 23.1331 (c) requires that for each instrument that uses a
power source, there must be at least two independent sources of
power (not driven by the same engine on multiengine airplanes) and
a manual or an automatic means to select each power source. CAR
(1998) 23.1 (1)(a) requires compliance with FAA 23.1331. However,
this regulation, and the FAA, only require compliance with the
amended FAR 23.1331 for aircraft certificated against that standard
(i.e. since March 29 1993). The vast majority of aircraft operating
in the USA and in Australia were certificated to earlier
standards.
FAR 91.205 states the instruments required for flight under VFR and
IFR conditions. This regulation does not require alternative power
sources for these instruments.
CASA has mandated CAO 20.18 APPENDIX IV for aerial work and private
operations. Para 3 of this appendix requires that specific
instruments have duplicated sources of power supply. Hence, CASA
has at present mandated a higher standard of alternative power
requirements than is mandated by the FAA.
CASA has therefore mandated FAR 23.1331 for new aircraft
certificated against FAR 23, and has retrospective requirements in
place which exceed the requirements implemented by the FAA.
