Alan Aldous, 42, of Normans Court, Micklefield Road, will be sentenced at Isleworth Crown Court on December 12.
He pleaded guilty yesterday to possessing a prohibited weapon, namely a stun gun, at the airport's Terminal Three on May 4.
The prosecution dropped a more serious charge of possessing a disguised weapon, which carries a minimum five-year prison sentence.
“He had a stun gun that had the appearance of a torch that had 'Stun Gun' written on the side,” said prosecutor Mr. Julius Capon.
Judge Paul Dugdale refused a defence application to sentence immediately and ordered a probation report, announcing: “I think it's important the court knows a little bit more about you and why you had a stun gun in your possession.”
Aldous was granted unconditional bail.