A passenger on an Alaska Airlines flight bound to Seattle looked out the window and saw what appeared to be a damaged area on the wing with a handwritten note saying: "We know about this."
The incident on July 28 drew comments on Twitter and other social media websites, but the Seattle-based airline says there was nothing to worry about.
Spokeswoman Bobbie Egan said today that it was an approved trim repair to the corner flap on the right wing. A maintenance technician wrote to let the flight crew know.
Egan said: "The message was the result of someone's good intentions," but the wing note "was not appropriate and did not follow company procedures".
The message was immediately removed and Alaska apologised for any alarm it may have caused.