What is the secondary command to checking static lines?

The secondary command for checking static lines, which is "Last two jumpers turn and face the skin of the aircraft," is critical for ensuring the safety and proper positioning of the jumpers during the exit sequence. This command instructs the last two jumpers to turn and face the aircraft's interior, allowing them to visually confirm that their static lines are properly connected and not entangled. This position also ensures that they can better coordinate their movements with the jumpmaster and each other as they prepare to exit the aircraft.

This specific command helps facilitate a safe exit by minimizing the risk of jumpers inadvertently interfering with each other's static lines or experiencing any complications during the jump. It also provides the jumpmaster with a clear view of the jumpers, allowing for a final check before they leave the aircraft.

In the context of the other options, the commands regarding ensuring the last jumper is secure, having all jumpers prepare to exit, and checking helmet straps are also important, but they serve different purposes. They are more related to overall readiness and safety checks rather than the specific action of checking static lines, which is uniquely addressed in the selected command.