One passenger, Abbey Desmond, from Essex, said a ripple of confusion passed through her plane as it approached Gatwick, which is about 95km from Luton Airport, with a long drive though or around London separating the two.
“I actually was in a state of panic,” she told The National.
“I genuinely thought ‘oh no, have I actually had another blonde moment and booked the wrong airport home now?’ but when we landed about a minute later and they said we were at Gatwick I had the biggest sigh of relief.
“Everyone was saying 'Luton' and thought we’d been diverted or gone to the wrong airport.”
Ms Desmond was returning to the UK from a holiday in Mexico when she looked out of the window and saw the welcome sign.
YouTube prankster Josh Fosh, who said he was inspired by similar stunts in Australia and the US, explained how he had managed to put the 60-metre-long sign in place.
“It's my job to make videos and my videos are all about doing silly things, to put a smile on people's faces but just to be silly," he said. "I'm glad this stunt has gone down well.
“I went door-knocking on fields next to Heathrow and Gatwick and a lovely couple said, “yeah, we've got a 80m long patch of land we don't have any use for”, so I said 'great, can I get my tarpaulin out and start hammering pegs into the ground?'”
Each of the letters is 8m by 3m and the sign, which Mr Fosh said should be in place for another six weeks, cost a total of £4,000.