Over at iFixit they have dissassembled the AR.Drone to see what makes the drone fly. Have a look at their teardown of the AR.Drone and learn how they judge the repairability of the AR.Drone.
Mine is currently back to Parrot for a repair because the main board appears to be broken. After replacing the central cross I got the “Motor Emergency” error message. After Googling for the error message just now I read that that error message might be related to the firmware. Supposedly downgrading the firmware might fix that problem. Anyone familiar with this problem?