An octagonal concrete shaft for a new control tower at O'Hare International Airport, Chicago, was erected quickly and efficiently using a jump-forming system both for exterior and interior wall construction. Unlike conventional gang forms, a jump form's wall gangs can be stripped and reset without being returned to the ground for cleaning and reoiling. On this project, the system significantly reduced crane-time requirements and allowed crews to achieve a cycle time of only five working days per lift. Using a 100-ton crane, workers were able to raise all eight exterior forms to the next level in just 30 minutes. The tower's 166.5-foot-tall concrete shaft was built in about four months using the jump-forming system and steel-framed modular form panels. Completed in June 1994, the shaft required a total of 16 lifts, most of which were 11 feet, 8 inches high. Yet to be built atop the shaft is a 750-square-foot steel cab for air-traffic controllers. The cab will be the largest in the United States, reflecting O'Hare's position as the world's busiest airport.