What initiates the movement of the seat during the ejection process?

The initiation of the seat's movement during the ejection process is primarily due to detonated gas pressure. When the pilot pulls the ejection handle, a sequence of events is triggered that includes the firing of a propellant charge. This produces gas at high pressure, which then drives the ejection seat upwards and away from the aircraft. The rapid expansion of gases is essential for creating the necessary force to propel the seat and the pilot to safety.

While other options involve mechanisms that can contribute to different phases of the ejection sequence or are components of the system, they do not directly initiate the movement of the seat itself in the same critical way as gas pressure does. For example, the manual pull of the ejection handle is an action that starts the entire sequence, but it is the detonated gas pressure that actually provides the force necessary for ejection. Therefore, the correct understanding is that it is the gas pressure resulting from the detonation that initiates the movement of the seat.