Steve Lewis, a Jet2 passenger snapped a photo of a beer can sitting next to a pilot, which was sitting there for about 20 minutes while people were unloading.
A spokesperson for the airline said: "Upon further investigation of the photograph, we can confirm that it is an unopened can which had been handed to a member of our cabin crew by a customer when they were leaving the aircraft.
"This unopened can was then put down in the cockpit by the member of cabin crew, so that she could continue helping customers as they disembarked."
But, Steve said he was not reassured, adding "It concerns me that alcohol is even allowed in the cockpit, if it was open or not.