From CNN Correspondent Jennifer Auther

(CNN) -- The crash of Swissair Flight 111 off Nova Scotia this week undoubtedly weighs heavily on the minds of people who already fear flying.

Anxiety experts said most phobias, including fear of flying, begin with a kernel of actual threat.

"It makes everybody worse, and the reason is people relate to that. Everybody's been on that particular flight, in their mind," said clinical psychologist Dr. Rodney Boone.

Even flyers who aren't normally afraid have much to contemplate this week.

In addition to Wednesday's Swissair crash, which killed all 229 people aboard, there was a fatal, mid-air collision Monday of two non-commercial planes in Wisconsin and a near collision involving two commercial jetliners in Southern California, also on Monday.

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The incidents have raised concerns among air traffic controllers.

"We need more air traffic controllers to be able to function safely," said Hamid Ghaffari, a controllers' union representative.

In Phoenix, picketing America West mechanics said they are worried about passenger safety because airlines are contracting out maintenance work.

Instead of worrying about these developments, fearful flyers are encouraged to consider the odds.

"The odds are overwhelmingly in your favor that you're going to arrive at your destination without problems. So, the fact that you have this huge anxiety reaction is a false alarm reaction," Boone said.

The most important thing for phobic flyers to do is to board a plane again, he said.

"We've got to get them back in that situation. We've got to get them flying again," Boone said.