John Wayne Airport is a Critical Facility providing international airline services to Orange County and the surrounding Southern California area. West Coast Air was able to construct a completely new Co-Gen Facility without interruption of critical airport services required to be operational 24 hours a day 7 days a week. The luxury of a completely new construction site allowed the existing cooling tower system to remain functional during construction but the tie-in to the existing condenser water system had to be seamless to avoid any disruption. The new condenser water system had to be completed including all commissioning and functional testing prior to taking the old condenser water system off-line. To do so, the existing condenser water headers were isolated by existing valves when the cut over occurred. A one-hour outage was requested 40 days in advance for all airport services to prepare for the short outage. The cut-over was performed seamlessly during an early morning time period requiring minimal airport functionality and was a complete success.