A KC-135 aircraft was pressurized at ground level with its outflow valves capped, which are meant to regulate pressure. During a five-year overhaul, the valves were never opened. An investigation found that a technician used a homemade gauge and no procedure to pressurize the plane, as he had "always done it that way." As the gauge's needle went around for the second time, the rear hatch blew over 70 yards away. This incident occurred because standard procedures and checklists were not followed. It serves as a lesson to have trained staff using proper tools and following detailed instructions, even if something has always been done a certain way before.