U.S. Air Force Airman 1st Class Phillip Clark of the 158th Fighter Wing replaces the Environmental Control System boot on a F-16 Fighting Falcon on March 8, 2014, at the Vermont Air National Guard base. The ECS boot, attached to the high stage bleed air shut off valve, channels the air off the F-16 engine to provide the cabin with air condition. (U.S. Air National Guard photo by Senior Airman Jon Alderman)