The term "al-qaeda" is a media invention. It was made up in order to pretend that all the world's radical militants had suddenly joined forces into an organized and powerful group.
From 9/11 until today, there have been a total of 6 planes targeted by "terrorists" in the United States, out of more than 10 million flights by commercial jetliner. Though it was more dangerous than any previous decade for air travel, a lower than 1 in a million chance of being targeted by a terrorist is in fact remarkably safe. It's much lower than the chance of the plane crashing for other reasons. It's even lower than the chance of the pilot being drunk.
Since I was a math major in college and you clearly were not, I'll put this in perspective for you. If you live 75 years, that's a total of 27,375 days. If the probability of any given plane being hit by terrorists were 1 in a million (remember, it's really lower), and you were to take one plane trip every day for your entire life, your chances of making it through all 27,375 trips without incident would be 999,999/millionths to the power of 27,375,
0.999999 ^ 23375 = .97299
about 97.3%. So your chances of at least one attempted attack would be 2.7%. That's lifetime risk, and only if you take a plane every day. If that seems high, remember 75 is around US mean life expectancy, so in general you have a 50% chance of dying by 75 in the first place, and the 2.7% includes non-fatal attacks too. More realistically, if you take 10 plane trips a year on average, then your risk would be
1 - 0.999999 ^ 750 = 0.00075
or a paltry 0.075% lifetime chance of ever being targeted by a terrorist. Note that the numbers include the attempts of dorks like Richard Reid and the latest "attacker," who can't even manage to detonate their devices.
So if you take 10 plane trips a year till age 75, you have a 0.075 percent chance of terrorists trying to kill you at some point, but a 50 percent chance of dying anyway from something else.
But so many people died in 9/11, right? About 3,000. Well, if you considered the US population as a random sample, that would have given you a 0.001% chance of dying in that attack, which was the worst single-event terrorism risk the country is ever likely to face. For some more perspective, during 2001 and most years since, over 14,000 Americans have been murdered each year by other Americans; more than that have been killed by their own selves, either through suicide or accident; and hundreds of thousands every year by their own bad eating habits and lack of exercise. 19,000 Americans are killed every year by staph infections they catch in hospitals. 3,000 is also dwarfed by the number of Americans who die every day from all causes.
Auto accident deaths exceed many times over the greatest damage ever managed by terrorists, but I doubt you're afraid of your car. I also doubt you're truly afraid of the drunk driver who might be in the other lane, even though they're responsible for half the auto deaths. Since so many more Americans are killed by drunk drivers than by terrorists, by your logic law enforcement has failed to deal with drunk driving as well. Maybe we should use the army to catch drunk drivers. It would be a lot less expensive, and much more effective at preventing american deaths.
If you're still scared of terrorists after all this common sense, you're doing exactly what they want you to do. Or maybe they're doing what you want them to. Like teenagers at a zombie movie, you want to be scared, or you'd be bored. Drunk drivers and staph infections don't make for scary TV, do they?