What secures the BAK-15 stanchions in an upright position when elevated?

The mechanism that secures the BAK-15 stanchions in an upright position when elevated is the over-center locking arm mechanism. This design utilizes a hinge point that, when the stanchion is raised, engages the arm in such a way that it locks in place, forming a secure connection that prevents the stanchion from collapsing. The over-center mechanism relies on the principles of leverage and gravity to ensure stability, making it a reliable choice for maintaining the stanchion's position during operations. This functionality is essential for safety and operational effectiveness in environments where the stanchions are used, such as in aircraft deployment and maintenance scenarios.

The other options do not fulfill the requirement for locking the stanchions in place as effectively as the over-center locking arm mechanism does.