Some of the most intriguing cover-up operations designed to keep construction going full-force throughout the winter months involve the use of air supported structures- gigantic air bubbles, if you will. One such air supported fabric structure was used over the site of Trans World Airlines' new 747 jet engine test center at the Kansas City International Airport. Phoenix General Construction Company workmen on this 3 million dollar project were able to place concrete when outside temperatures got down to 10 degrees. This 650,000 cubic foot "super bubble" boasted such working features as a 100- by 200 foot clear span interior, and a height of 50 feet. This allowed ample room for construction work, including the erection of necessary scaffolding. Two 7 and one-half centrifugal blowers were used to inflate the structure and to maintain the low pressure differential needed to support and tension the 26-ounce per square yard fabric. Normally only one blower is required to maintain adequate air pressure, but a second is usually retained as an emergency standby.