The cloud seeding that has occurred above the Medford Airport for a half-century has come to an abrupt end.

The cloud seeding that has occurred above the Medford Airport for a half-century has come to an abrupt end.

Pilots have taken to the air above the Rogue Valley on foggy mornings and evenings since the 1950s to create holes in the fog, allowing commercial airliners to use the airport.

Airport Director Bern Case said changes in Federal Aviation Administration regulations led the Jackson County-owned airport and Medford Air Service — which performed the seeding — to discontinue the work.

"Safety is the issue," Case said. "There was a time when a cloud-seeding plane could make a hole and land in its own hole. Now, under instrument flight rules, they are required to do same thing as commercial airliners."

That means the Cessna aircraft used for seeding would have to fly 25 miles out from the airport and then follow the same landing approach as the commercial planes before being allowed to return to the ground at Medford.

"If the hole closes up (in the interim), the pilot can't land," Case said. "We don't have a great alternate. If Ashland is closed that means they have to fly out of the area."

Although both the FAA and airlines employ advanced navigational technology, seeding often made the difference between flying and grounding aircraft.

Commercial liners will bear the largest cost through flight cancellations and delays as a result of the change.

"It's a hard thing to put a number on it, but there will definitely be a few more cancellations and a few more delays," Case said. "It's hard to tell what the front-end costs will be for the airlines."

The practice was pioneered in Medford by the late George Milligan — best known for founding the air ambulance company Mercy Flights — during the late 1950s and became a staple to keep air traffic flowing.

Milligan and Wayne Reavis, a retired fixed-base operator, developed a routine of flying above the airport and dropping dry ice pellets when freezing fog formed at 31 degrees.

The fog's temperature must be below freezing in order for cloud seeding to be successful. Water molecules won't stick to the dropping ice pellets.

The object of seeding is to provide the necessary visual range for planes to land — about 1,300 feet for some jetliners and 1,800 feet for others. Commercial flights heading for Medford sometimes circled during the process, rather than diverting to other destinations.

"December is a tough time for us," Case said. "When aircraft is up there it can get iced if we make them fly around indefinitely."

Medford was the last airport in the country to employ the practice. Salt Lake City discontinued cloud seeding two years ago. Seeding continued locally through last week with multiple applications on foggy days.

"We've tried to work with the FAA, but they're a big organization and regulations are regulations," Case said. "The rule (requiring cloud seeders to fly out and back) has been on the books quite awhile. We've been given some leniency and the leniency has evaporated."

The county had a contract with Medford Air in which it would spend up to $27,000 between November and February, including $2,000 monthly for stand-by services. The hourly rate for seeding was $375, plus the cost of the ice.

"Medford Air was one of the last facilities to provide this kind of service and we're proud of what our crews have done," said Cyndi Ash, general manager at Medford Air Service. "We determined it was a good time to end it."

She said Medford Air had made fewer than 10 seeding flights this season.

While Case said the search is on for other ways to improve winter visibility at the airport, there was no immediate alternative to cloud seeding.

"It's a safety issue more than anything else," Case said. "The time of exposure is part of the issue. (Medford Air has) great pilots, who can make an instrument approach. But this is the right thing to do. I wouldn't want to have to put out a release about a disaster."

Reach reporter Greg Stiles at 776-4463 or e-mail business@mailtribune.com.