Air passengers have been left panicked and confused after a "Welcome to Luton" sign appeared near Gatwick Airport.
The 60m (197ft) sign is visible on the approach to Gatwick - which is about 60 miles south of Luton.
Abbey Desmond, from Great Dunmow, Essex, said when she spotted it out of the window on landing it left her in a "state of panic".
The stunt has been claimed by YouTube prankster Max Fosh, who apologised if "anyone has been seriously thrown".
Admitting to the prank on the Justin Dealey show on BBC Three Counties Radio, Mr Fosh, who has 923,000 followers, said: "I am the pesky prankster that has written Welcome To Luton."
He said it had caused some confusion with one woman messaging him to say she was worried she was in Luton as she had left her car at Gatwick.
Others on Twitter admitted it had caused confusion.
The inspiration came from similar stunts carried out in Australia and the USA, Mr Fosh said.
"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, I'm glad this stunt has gone down well."
Ms Desmond saw the funny side of it and posted the photo on Twitter, to "give everyone else a laugh and it has blown up with everyone blaming RAF Luton".
Her post has received more than 20,000 likes.
RAF Luton is a parody Twitter account about "the world's most mysterious and secret (and fictitious) military base".
Explaining how he carried out the prank Mr Fosh said: "I went door knocking on fields next to Heathrow and Gatwick and a lovely couple said, 'yeah we've got a 80m (262ft) 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?'."
Placing 14 letters that are 8m (26ft) by 3m (10ft) cost him £4,000 as it has been "made to last", he said.
He currently has permission for the words to be there for six weeks, so "if you're flying into Gatwick have a look out your left window you should see it about 90 seconds before landing."