Which power sources supply the two FADEC channels during engine start, and how do they operate?

Which power sources supply the two FADEC channels during engine start, and how do they operate?

• A. EMER bus prior to engine start 45% N1, PMA during engine start after 45% N1, with the channels alternating
• B. Battery only
• C. APU bleed
• D. Ground power unit

Answer: (A)

Two FADEC channels must stay powered by independent sources during start to guarantee continuous control if one source falters. Before engine start, the FADEC channels receive power from the EMER bus. This ensures the units remain powered even if main electrical sources aren’t online yet. As the engine spools up and hits about 45% N1, the engine’s permanent magnet alternator (PMA) takes over powering the FADEC channels. The PMA feeds the two channels in an alternating fashion, which provides load sharing and checks both channels for proper operation during start. This arrangement keeps both channels alive and ready for full flight operations. Using only a battery wouldn’t provide the required redundancy and power reliability for the FADEC during start, and external sources like an APU bleed or a ground power unit aren’t the intended sequence here.

Two FADEC channels must stay powered by independent sources during start to guarantee continuous control if one source falters. Before engine start, the FADEC channels receive power from the EMER bus. This ensures the units remain powered even if main electrical sources aren’t online yet.

As the engine spools up and hits about 45% N1, the engine’s permanent magnet alternator (PMA) takes over powering the FADEC channels. The PMA feeds the two channels in an alternating fashion, which provides load sharing and checks both channels for proper operation during start. This arrangement keeps both channels alive and ready for full flight operations.

Using only a battery wouldn’t provide the required redundancy and power reliability for the FADEC during start, and external sources like an APU bleed or a ground power unit aren’t the intended sequence here.