How is electrical system redundancy achieved on ATR aircraft?

• A. A single generator powers all essential systems.
• B. Multiple generators, a standby power source, and essential/equipment buses with isolation.
• C. Only external power is used.
• D. The battery alone supplies all critical power.

Answer: (B)

Redundancy in the electrical system means keeping critical power available even if one part fails. On an ATR, this is achieved by using more than one source of power, plus a dedicated back-up, and by organizing the loads so a fault doesn’t bring down everything.

There are several generators: multiple engine-driven generators and an APU-generated source. This means if one generator drops out, others continue supplying power to essential systems. In addition, a standby power source provides a guaranteed back-up to the essential electrical bus, so vital items like flight instruments, navigation, and communications can stay powered even if main sources are unavailable. The loads are split into essential and equipment buses with isolation, which lets the system separate a faulty circuit or bus from the rest, preventing a failure from cascading and ensuring critical systems remain powered.

External power on the ground is possible, but in flight the design relies on these multiple internal sources and isolated buses for true redundancy. The other options rely on a single source or on external power only, or on the battery alone, which wouldn’t provide the needed reliability and duration for critical systems.