An airline boss has admitted to "multiple failures" after a boy managed to board one of its planes without tickets during the security alert.
The boy passed through all security checks in the airport building
The 12-year-old, believed to be from Penrith in Cumbria, was found on Monday's 0600 BST Monarch flight from Gatwick Airport before it took off.
Tim Jeans, managing director of Monarch Airlines, said there were issues that "must and will be addressed".
Airport operator BAA said the boy had passed through security procedures.
Mr Jeans added: "I think it's equally important that the final line of security did work.
"That's the check when passengers get on board the aircraft and their boarding cards are checked but of course it shouldn't have got that far."
Chris Garton, operational solutions director for BAA at Gatwick Airport, said a full investigation was being carried out with the police and Monarch Airlines.
"We are aware that the boy was identified without documentation but we're absolutely confident from the investigation so far that he was thoroughly searched and passed through the full security screening process," he said.
"The main issue for me is to reiterate to our travellers and to our customers that at no time was there any threat to passengers, staff or to the aircraft."
The boy, who took a train to Gatwick Airport after running away from a privately-run care home in Wirral, Merseyside, was heading to Lisbon.
Staff only realised the boy was a stowaway after he had sat down and been served with a soft drink.
A spokesman for Wigan Metropolitan Borough Council, which is responsible for his care, said: "He is not permanently confined to the home and the police were alerted as soon as it was realised he had absconded.
"We will be reviewing his care arrangements and any future risk management issues."
The Commission for Social Care Inspection backed the care home, but said increased supervision was now in place.
Conservative MP and former shadow home secretary Ann Widdecombe said she found it "perfectly flabbergasting" the boy was able to board the plane.
She said: "He could get through the whole lot including boarding the plane itself before anyone discovered that he hadn't got a passport, hadn't got a ticket, hadn't got a boarding pass, hadn't got an anything.
"It would be amazing any time and any place but in the present climate that really is amazing."
Meanwhile passengers at Gatwick Airport are continuing to experience disruption with 11 British Airways domestic flights from the airport cancelled on Wednesday.