What is the first step you must take when responding to a trouble call for an inoperative freight door?

When responding to a trouble call for an inoperative freight door, the initial step is to check the power supply. Ensuring the power supply is functioning correctly is crucial because many issues with operational malfunctions stem from an inadequate or interrupted power source. If the power supply is intact, it allows for further troubleshooting, such as inspecting the motor, without assuming the door's mechanism is faulty.

Blocking the door open is not a priority method to diagnose the issue and could potentially create safety hazards. While calling for assistance may be necessary in certain situations, it's essential first to establish whether the operational failure is due to a power issue, as resolving power problems can often restore function without escalating to more complex checks.