What is the role of a sequence valve in a hydraulic retractable landing gear system?

In a hydraulic retractable landing gear system, the sequence valve plays a crucial role in controlling the order of operations for deploying and retracting the landing gear and its associated gear doors. This ensures that the landing gear and the gear doors function in a coordinated manner. For instance, when the landing gear is retracted, the gear doors must close first before the gear itself starts to retract, preventing any potential damage or malfunction. Conversely, during deployment, the gear must extend before the doors open, ensuring that the gear is properly positioned before the doors facilitate a smooth transition.

This ordered sequence is vital for safe and effective landing gear operation. If the sequence were not controlled properly, it could lead to malfunctions, such as the gear not fully extending or the doors obstructing the gear's movement. Therefore, the sequence valve is essential in maintaining the integrity and reliability of the landing gear system, making option C the correct answer.