The Scot was at London's Heathrow Airport when he first spotted a pretty young lady, who he had his eye on and then tried to chat her up during the flight to LAX.
An onlooker told UK newspaper The Sun: 'Most of the lads at Terminal 5 never even noticed Gerard to start with because the woman was a jaw-dropping stunner.
'She was turning heads. A tall, early twenties, model-looking brunette. Gerard was swept through the queue with officials for the airline and boarded the plane.
'He spotted her and nearly fell over. It was a classic double-take. He should have had a yellow card for the look he gave her.'
The source added: 'When we boarded she was a few rows in front of us in 42B. You could see him peering back from first class.
'Then 15 minutes later one of the airline's ground staff came along, handed her a piece of paper and gave her a wink. It was priceless. All the lads on the flight laughed and she blushed and started giggling.
'We didn't see what happened when we got off at the other end.'