When is the Cockpit Voice Recorder powered on?

The Cockpit Voice Recorder (CVR) is designed to operate whenever the aircraft is powered and in use, starting from the moment DC electrical power is applied to the aircraft. This ensures that all important audio data from the cockpit is captured throughout all phases of flight, including preparations and taxiing on the ground, as well as during flight. By powering the CVR with the application of electrical power, it can continuously record vital conversations and sounds, thereby enhancing the ability to investigate incidents or accidents.

While the other options might seem plausible, they do not fully encompass the operational readiness of the CVR. For example, the CVR being active when the engines are running does not capture scenarios where important communications occur prior to engine start-up. Similarly, its operation strictly "on the ground" would miss crucial voice recordings once the aircraft begins to taxi or take off. Closing the cabin doors typically impacts systems related to environmental control and passenger safety rather than the CVR itself. Therefore, the comprehensive capability of the CVR being powered on with the application of DC electrical power is critical for thorough functionality throughout all operational periods of the flight.