The green trend is taking hold in the airline industry.

United Airlines announced plans in June to buy 15 million gallons of lower-carbon, renewable jet fuel over a three-year period.

And Alaska Airlines is testing solar-powered passenger ramps.

The mobile ramps used to get passengers on and off planes are equipped with solar panels that power the batteries that drive the ramps’ electric motors. Traditional mobile ramps and passenger stairs are powered by gasoline or diesel engines.

Alaska has been testing the ramps at Seattle-Tacoma International Airport and Norman Y. Mineta San Jose International Airport.

If the weather doesn’t cooperate, the solar ramps can be plugged into an electrical outlet, said Michael Keith, sales manager for Keith Consolidated Industries in Oregon, which built the ramps.

"They are extremely efficient," he said of the ramps. "There is a lot of savings, not just in fuel, but in emissions as well."

Frontier might follow Spirit’s lead

Get ready for the takeoff of another supercheap airline offering ultralow fares with loads of passenger fees.

Industry insiders say the new superdiscount airline may soon be launched with the help of Indigo Partners, the Phoenix private equity firm that invested in Spirit Airlines in 2006.

Indigo is reportedly negotiating to buy Frontier Airlines from the Denver carrier’s parent company, Republic Airways Holdings Inc.

"They really are taking the Spirit Airlines playbook from Florida to Denver," said Henry Harteveldt, a travel analyst with Hudson Crossing in New York.

Indigo officials did not respond to requests for comment, and Republic Airways representatives would only say that they expect to sell Frontier to a "third-party purchaser" by September.

–Hugo Martin / Los Angeles Times