^ I’m just guessing, but I recon a very high percentage were on merit scholarships. The engineering field tends to draw in those high-stat kids anyway; the scholarships just attract them to UA. 
Most of these students who drop out of aero have not ‘failed’, in terms of losing their scholarship - many realise eng’g is not for them…some change majors within eng’g and do mechanical instead, e.g.,…and still others leave the university entirely for a variety of reasons. Later on, like a year later, when the much harder classes kick in…that might be when you start to see students more in danger with their scholarships and dropping for that reason, but I bet that is much rarer. Students know pretty darn quick (esp in aero, like after 1 semester) if it’s for them or not! They don’t (usually) hang about hoping it will get better or easier or more interesting. The College of Engineering may be able to help give you some insight, too?
I’m going to post again my fave site for comparing apples to apples when it comes to eng’g schools. Use this profile search tool to see bums on seats for any program, any school, any year, as well as how many actually graduate: http://profiles.asee.org/profiles . Happy digging!