Emergency procedure alpha two

From Memory Alpha, the free Star Trek reference

Emergency procedure alpha two is the act of bypassing main computer control and switching all systems to manual override. This is a procedure that is performed onboard Starfleet vessels in dire situations when the main computer is offline.

When the USS Enterprise-D was severely damaged after colliding with quantum filaments, Chief Miles O'Brien initiated this procedure on the main bridge in order to regain control over the ship. (TNG: "Disaster")