If fitted and actuated, the EMER SW cuts all DC power except for the following items powered direct from the battery: Engine, NR/Nf instrument, Emergency lighting (Map lights). The systems description (Page 7-31 in the RFM) states:
In case of an electrical emergency, after actuating the [EMER SW] (If fitted) in cut-off (down) position, all DC power is switched off except some vital consumers directly fed by the battery:
- The engine,
- NR/Nf instrument,
- Emergency lighting (Map lights)
It's used for Smoke In Cockpit / Cargo emergency drills etc.