When applying external power, which precaution is correct?

• A. Mobile power unit is chocked and facing away from the aircraft
• B. Ensure the circuit breakers and switches are positioned to receive power
• C. Inspect power cables and cable assembly for corrosion
• D. Personal danger area during APU operation

Answer: (A)

When applying external power, the most important precaution is to secure the mobile power unit so it cannot move and to position it so hazards are directed away from the aircraft. Chocking the unit prevents it from rolling or shifting during the power connection, which protects both the aircraft and personnel from potential contact, damage, or tripping hazards. Having the unit facing away from the aircraft helps keep exhaust, heat, and any belt or vibration effects directed away from the airplane and the crew, reducing exposure to heat, fumes, or sudden movement.

While other steps like verifying circuit breakers and switches or inspecting power cables are important parts of overall electrical safety, they do not address the immediate risk of uncontrolled movement and exposure when power is applied. The option about a personal danger area during APU operation is not applicable to the external power scenario, since it references the APU rather than an external power unit.