COLORADO SPRINGS — With the ability to drop nearly 20,000 gallons of water or retardant in a single pass, the Global SuperTanker could be an airborne, blaze-battling behemoth on the front lines of the 416 fire near Durango — or any of the other wildfires burning in Colorado this week. But the converted Boeing 747-400, which started life 26 years ago as a Japan Airlines passenger jet, instead sat Wednesday on a runway at Colorado Springs Airport, its engines off and its cockpit empty.