A video clip lesson learned on the topic of Process Control. Actuators inside the tail enable the rudder speed brake panels to steer and slow the Space Shuttle during descent and landing. Unusual wear was found on the planet gears of the actuators during an inspection. This led to a discovery that when the Shuttle was built the gears were installed incorrectly¿ a critical flight failure mode. The installation error stemmed from the near identical appearance of component gears that had different design topographies. The robust actuators were able to operate for 20 years (approximately 30 missions) without failure. The mistake was not found sooner because the actuators were certified for the original flight life of the Shuttle¿ 10 years or 100 missions. New gears were installed, and a process control was implemented that accommodates the demands of ground operations. A dedicated fixture was fabricated for each actuator with physical features that prevent installation of the incorrect gear. Designs should be mistake-proofed so that components cannot be assembled incorrectly. This 4-minute, 33-second video is a product of the Space Shuttle Program and its Process Control Focus Group.