My friend is both double majoring in Flight and Economics. He's also partaking a number of research projects through the AT department, on top of working the student advising office correcting people's resumes/cover letters. I honestly don't know where he finds the time. I really think he's a lot more smarter than he lets on. Oh yeah, he's only a sophomore.
Anyhow, it is possible to double major. Like Jason said, it's all about your work ethic. It would be tough to graduate in 4 years, unless you really put the petal to the metal (take >20 credit hours per semester).