This week, British Airways confirmed that terrorist fears are having an impact on bookings.
Many airlines offer courses to tackle a flying phobia
With planes being grounded and security checks being stepped up, that is perhaps unsurprising.
But behind the drop in bookings lies a common fear. BBC News Online examines why so many of us are afraid of flying.
"I used to get very panicky," says Anna Ferguson.
"I'd get anxious. I'd feel dizzy. I'd walk around in a daze."
Anna has been afraid of flying for more than 30 years.
She can trace her fear back to a bad experience on a plane when she was just 11 years old.
But rather than get better over the years, her fear has actually become worse.
In July 2001, Anna, who lives in London, cancelled a dream holiday to Miami.
"I just couldn't do it. I was having horrible dreams. I was really upset," she says.
Two months later, two planes crashed into the World Trade Centre in New York. Needless to say, Anna hasn't been on a plane since.
As many as one in four people may be afraid of flying. That figure is believed to have increased sharply in the aftermath of September 11.
For some people, a stiff drink in the departure lounge is enough to quell their fears.
For others, the problem is much more deep-seated. Even the thought of sitting on a plane is enough to trigger a panic attack.
This is despite the fact that travelling on a plane is much safer than getting into a car.
Figures from the United States National Safety Council suggest the risk of dying in a car is up to 37 times greater than from flying.
"Fear of flying is probably the commonest phobia we see in our clinic," says Professor Paul Salkovskis, director of the anxiety disorder and trauma clinic at The Maudsley Hospital in London.
"It is essentially a phobia. People with this phobia are afraid that the plane will fall out of the sky. They are afraid they will get trapped."
A phobia is an irrational fear of a certain object, situation or activity.
"There are basically two types of fear of flying," says Sue Morris of the National Phobia Society.
"The first can be triggered by a specific event such as 9-11. People suddenly become aware of how vulnerable they are on a plane and become worried about it crashing.
"The second is a fear of being trapped and not being able to get back to safety.
"A lot of people have this anxiety on a low level. After all, very few people say they actually enjoy flying.
"The problem occurs when this anxiety gets out of control."
Many people suffer from this second type of fear. They readily admit that their phobia is irrational and has no logical basis. However, they are still powerless to overcome it.
Scientists around the world are carrying out research to try to find out what happens in the brain to trigger such an irrational response.
They have yet to come up with a definitive answer. Recent studies have suggested genes may make some people more susceptible than others.
Of course, people who are afraid of flying can simply opt to avoid planes.
They can keep their feet firmly on the ground and still get to where they want to go using cars, trains and even boats. However, others are keen to beat their fear.
Counsellors, psychologists and hypnotherapists all claim to be able to offer a cure. Many airlines offer one day courses to help potential passengers to get on board.
The medical evidence suggests the best way of overcoming a fear of flying is to face it.
"The only treatment shown to be effective is cognitive behaviour therapy," says Professor Salkovskis.
"This is essentially getting people to confront their fears.
"In our clinic, patients with flying phobia have between three and five sessions of cognitive behaviour therapy.
"With high quality cognitive behaviour therapy, you can expect up to 70% of patients to see their fear disappear."
That's not to say other approaches don't work. The National Phobics Society has anecdotal evidence that hypnotherapy can help many people.
"A course of hypnotherapy, lasting maybe three to six sessions, can help to reduce anxiety levels," says Sue Morris.
However, what works for some people may not work for others.
Anna Ferguson has spent the past two years trying to overcome her fear.
"I am trying to cure myself of this phobia. I have been on a one-day course run by an airline but that didn't work.
"I am now going to group therapy sessions to try to beat it. I refuse to give up."