'Inversion' Keeping Planes from CA Firefight

July 30 -- A thick layer of trapped smoke is challenging efforts to contain the fierce Carr Fire in Shasta County, keeping critical aircraft on the ground.

Air tankers — rumbling pot-bellied planes that drop protective red streaks of retardant from the sky – are among the most welcomed sights in fire-ravaged communities.

The aircraft can access steep, rocky or unsafe areas before ground forces are able to gain entry. And once planes suffocate the flames, it is safer for these ground forces – primarily bulldozers and chainsaw-wielding hand crews — to get close to the fire line and get to work.

But this week’s weather phenomenon, called an inversion, means the aircraft can’t fly.

The Shasta County smoke, clinging near the ground, is so dense that planes lack the visibility to fly safely or spot the flames, said Cal Fire Deputy Chief Scott McLean.

“There’s a blanket of smoke. It’s been socked in for several days,” said McLean. “They need a flight path. They have to see the ground to be able to make drops or see obstructions.

The northern stretch of the Sacramento Valley is prone to inversions because of its terrain, said climate scientist Daniel Swain of the University of California at Los Angeles.

“It is a bowl, surrounded on three sides by mountains. It is only open to the south,” he said. “The air is stagnant at the top, the north end, of the valley.”

Normally, as air rises in altitude, the temperature decreases. In an inversion, the opposite is true: instead of getting cooler at higher temperatures, the air is actually warmer. This warm air “caps” the cooler air, causing smoke to hang low to the ground.

The blanket of smoke may be thicker than 1,000 feet, far higher than these planes fly, he said.

The missing aircraft fueled rumors that Cal Fire lacked the resources to effectively fight fires, frustrating residents.

“Fire fighting aircraft requests across California today are going unfilled, no state or Federal fixed wing available anywhere,” alleged one Tweet.

Cal Fire has the largest state-owned firefighting air fleet, with 23 air tankers, 11 Super Huey helicopters and 14 air attack aircraft. An air tanker — typically a refurbished passenger plane with retardant stored where passengers would have sat — carries 1,200 gallons of retardant, loaded at Sacramento McClellan Airport. Helicopters are fitted with a tank or carry a bucket with water or fire retardant and deliver a nine-person fire crew wherever is needed. The air tactical planes direct others where to go. California also has access to the Global SuperTanker, a retired Boeing 747 that is the world’s largest firefighting airplane, but that plane has returned to Detroit to have its engine replaced.

All this firepower is worthless if it can’t navigate. While commercial aircraft can handle low visibility situations, Cal Fire’s aircraft can’t.

Commercial aircraft fly thousands of feet high, at speeds of 300 to 600 miles per hour, with high-tech instrumentation. They know exactly where they are, and know the terrain below. In an emergency, they can find an airport.

“But tankers are flying between mountains,” said Bill Gabbert, managing editor of Fire Aviation magazine. “They’re flying lower and slower than commercial aircraft, dropping retardant around 130 to 200 miles per hour. There is no way to enable safe landing at an airport.

“There is always smoke in fire, but it is usually a column that rises,” he said. “Not thick, over a large area, where you can’t see the ground.”

Trapped smoke can sometimes lift during afternoons, after the sun heats the earth’s surface. That heat warms the air near the ground, which begins to rise and mix with cleaner air above.

“If there’s an opening in that cloud of smoke, we can go,” said McLean. “We are at the ready.”

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