Doctors said Edward A. Coburn, 32, of Fresno, California, was delusional when he broke through the cockpit door in October 2001 and screamed that the pilots were planning to crash the jet into Chicago's Sears Tower. Crew members and passengers tackled Coburn, bound him and held him for authorities.
Coburn, who participated in the trial by closed-circuit television, is being held at a prison hospital in Rochester, Minnesota.
Defense attorney Brian Collins and Assistant U.S. Attorney John Lausch both asked the judge to find Coburn innocent by reason of insanity.
Two mental health professionals found that Coburn suffers from bipolar disorder, Collins said.
U.S. District Judge Charles Kocoras ordered Coburn to undergo further evaluation. At the next court hearing set for May 29 Kocoras could continue Coburn's confinement, release him under conditions of continued treatment or release him outright.