Sixty-one-year-old Philippe Jeannard of La Rochelle, France entered the plea Wednesday in federal court.
A sentencing hearing has not been scheduled.
Authorities said Jeannard unsuccessfully sought a seat upgrade on a Florida-bound US Airways flight on March 20 and later used a fraudulent Air France ID card belonging to an ex-employee to gain access to the cockpit, where he was found sitting in the jump seat behind the pilot.
Federal public defender Elizabeth Toplin declined comment on her client's motives but told The Philadelphia Inquirer that "he never meant to cause any problems."
