Amazing Video: Aerial Assault Team Battles California Fire

The U.S. National Guard has released a series of stunning cockpit videos from the aerial assault team battling the Rim Fire, which is tearing toward San Francisco's water supply and protected giant-sequoia groves.

The videos are from the 146th Airlift Wing, based at the Channel Islands Air National Guard Station in Port Hueneme, Calif. Viewers see a towering brown cloud of smoke and a wall of flames, and hear a blaring automatic landing-gear warning as the C-130 Hercules plane approaches the drop site for its firefighting load of retardant chemicals.

"The landing-gear warning is heard by the pilots in the C-130J only," according to a note posted with the video. "Because the 'J' is such a high-technology aircraft, disabling the audible warning has proven difficult. Lockheed, the [Air National Guard] and [U.S. Air Force] have determined a software solution and, with luck, will be integrating the fix before next fire season." [Video: Rim Fire Seen Through Airborne Firefighters Eyes]

California's Rim Fire has burned nearly 180,000 acres (72,843 hectares) since it started Aug. 17 in the foothills of the Sierra Nevada. Burning east and south into Yosemite National Park, the growing fire threatens the Hetch Hetchy Reservoir, the source of drinking water and hydroelectric power for San Francisco. The city and county of San Francisco are under a state of emergency because of the potential threat to the electrical and water supplies. The fire also threatens two of Yosemite's three groves of giant-sequoia trees.

The blaze was 20 percent contained as of Tuesday morning (Aug. 27). More than 3,600 personnel are battling the fire as it approaches Yosemite. Labor Day weekend is one of the park's most popular tourist weekends of the year, and one of its main western entrance routes, Highway 120, is closed due to the Rim Fire. The National Park Service's website has current fire information and closures.

The Rim Fire is one of six wildfires in California, Idaho and Nevada being fought by planes equipped with the Modular Airborne Firefighting System (MAFF), according to a statement from the National Guard. The fleet included aircraft from the Wyoming National Guard's 153rd Air Wing and the Colorado Springs Air Force Reserve Command's 302nd Air Wing.

The last three years have required above-average use of MAFF resources, the statement said. Since 1973, the heavy air tankers have averaged 210 air drops per year. But in 2012,Air National Guard crews flew 884 air drops and dropped more than 2.3 million gallons (8.7 million liters) of water or retardant, the National Guard said. In 2011, crews flew 443 missions and dropped 1.2 million gallons (4.5 million liters).

This year, crews had been called in for 378 air drops by Aug. 26, the National Guard said.

The specially modified planes release a burst of water or retardant over an area approximately 1,320 feet long by 100 feet wide (400 by 30 meters), which can provide critical fire breaks, the National Guard said.

Email Becky Oskin or follow her @beckyoskin. Follow us @livescience, Facebook & Google+. Original article on LiveScience.