Daredevil Nik Wallenda prepares for Grand Canyon high-wire act

EDITORS PLEASE NOTE: THIS EDIT CONTAINS MATERIAL WHICH WAS ORIGINALLY 4:3 Air boats produce the perfect conditions for Nik Wallenda's tightrope practice, blowing winds of up to 91-miles-an-hour -- that's nearly 150 kilometers per hour. SOUNDBITE: Nik Wallenda saying (English): "I've always trained for wind with air boats. They're all over the place when you're in Sarasota (Florida). I've got some great friends that have them, and it's the easiest way to create high, heavy, gusty winds." The daredevil crossed Niagara Falls in 2012 and now plans to cross a section of the Grand Canyon amid gusty winds. It's the highest tightrope crossing he'll attempt ... and it'll be without a safety tether. All Wallenda's stunts are in tribute to his great-grandfather, Karl Wallenda - seen here tightrope walking above the River Thames. Karl fell to his death in 1978 in Puerto Rico. Wallenda's Grand Canyon stunt will be broadcast live on June 23rd on the Discovery Channel.