Where is the ejection seat safety pin installed?

The ejection seat safety pin is designed to prevent unintentional activation of the ejection mechanism. Installing the safety pin directly into the ejection handle mechanism ensures that the seat cannot be ejected unintentionally while the aircraft is on the ground or during other critical operations. This is a crucial safety feature that protects pilots and crew from accidental ejection.

The other choices do not provide the same level of direct protection. For instance, placing a safety pin into the ejection seat MOR handle or the SSK selector valve would not adequately inhibit the activation of the ejection system. Similar reasoning applies to the ejection seat armrest; while it may be a component of the seat, it does not directly control the ejection mechanism's safety. Therefore, the installation of the safety pin directly into the ejection handle mechanism is the most effective method for ensuring safety when it comes to the ejection system.