Why a Skyhawk can roll off an Essex flight deck

How could an A-4 Skyhawk roll over the side of an Essex-class carrier?

A flight deck does not restrain a wheeled aircraft by itself; brakes and tie-downs must secure it, and an unsecured aircraft can simply keep rolling over the edge.

The answer starts with the physical simplicity of the accident: an aircraft carrier has a broad, flat deck and the Skyhawk sits on wheels. The deck itself does not stop an aircraft from moving. Brakes and tie-down fittings provide that restraint during ship motion and deck handling. If those measures are absent or ineffective, the aircraft can roll until it reaches the edge.