Originally Posted by Pilot Paul
They are electrically actuated, operated from the 28 VDC system. They are also heated (by 115 VAC) to prevent ice accretion although this only activates if the OAT is less than 15 degress C.
Actually, it is the engine intake flange that is electrically heated, not the bypass doors. It is heated when the bypass doors are open, the engine is running and the OAT is below +15.
We operate the bypass doors in conjunction with the other ice protection equipment when ever we're in icing conditions, i.e., below +5 in flight and with visible moisture present.