Joshua Petty White did not declare the gun when he arrived in Canada from the United States in March.
The gun was detected at airport security as he was trying to return to the U.S. the next day as part of a flight crew.
The U.S. Transportation Security Administration said White used his "known crew member" status to bypass security at Salt Lake International Airport.
White was fined $4,000. He has been put on administrative leave while investigations are carried out.
His lawyer, Willie de Wit, says seven other charges were dropped in a Calgary courtroom Tuesday.
He says White admitted to being reckless in bringing the gun across the border and forgetting to check his luggage.
The weapon was a Smith & Wesson Bodyguard .380-calibre handgun.
White is not part of the Federal Flight Deck Officer (FFDO) program, whose members are permitted to carry firearms on board planes, according to a senior U.S. official.
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