§29.1331 Instruments using a power supply

For Category A rotorcraft: (a) Each requi red fl ight i nstrument usi ng a power supply must have – (1) Two independent sources of power; (2) A m eans of selecting either power source; and (3) A visual m eans integral with each instrument to indicate when the power adequate to sustain proper i nstrument performance is not being supplied. The power m ust be m easured at or near t he poi nt where it enters the instrument. For electrical instrum ents, the power is considered to be adequate when the voltage is within approved limits; and (b) The installation and power suppl y system must b e su ch th at failu re o f an y flig ht in strument connected t o one source, or of t he energy supply from one source, or a faul t i n any part of t he power di stribution sy stem does not i nterfere wi th the proper supply of energy from any other source.