LONDON (AP) -- The 11-year-old boy didn't have a passport, didn't have a ticket, didn't have a boarding pass, and got all the way from England to Italy on his own.
For him, the 1,000-mile (1,700-kilometer) journey was a great adventure -- and his excitement led to his discovery.
"He was chatting away about being off by himself," and passengers alerted the cabin crew, Russell Craig, a spokesman for Manchester Airport, said Wednesday.
The boy, who is known to be fascinated by transport and has a history of catching free rides on trains and buses, was sent back to Manchester on the return flight, Craig said.
For the airport, airline Jet2.com and the British government, Tuesday's incident was an embarrassing breach of security days before the start of the Olympics.
Ben Vogel, editor of HIS Jane's Airport Review, said he wasn't familiar with all the details of the Manchester incident but said it's a fundamental security principle that people aren't allowed aboard an aircraft if they have no right to be there -- whether or not they passed through a security scanner.
"It's not good, is it?" he said. "It is a security breach, if a non-threatening security breach."
An undisclosed number of security staff employed by the airport and airline employees have been suspended while authorities investigate.
"This is an unusual and serious breach and we are keen to find out what has gone on," said the government's transport secretary, Justine Greening.
Airport manager Craig, however, said "it's not technically a breach of security" because the boy did go through the normal security scan.
"The boy was no threat to the aircraft," he said. But he admitted the boy passed through five security checks before boarding the plane.
The first check came when he entered the secure area where an airport security officer is supposed to verify that the traveler has a boarding card or a staff pass.
"The boy arrived at security at a time when it was extra busy, there were a lot of families traveling," Craig said. While it's common for one member of a family to present all the boarding cards, he said, the officer failed to count to ensure that the number of cards matched the number of people going through.
The airline was responsible for four further checks on boarding, Craig said: for a passport, for boarding pass, another check at the aircraft door for a boarding pass stub with a seat assignment, and a final passenger count after everyone had boarded.
Manchester Airport is the third busiest in the United Kingdom after London Heathrow and London Gatwick. The security staff is hired and managed by airport officials.
The Manchester Evening News quoted Sarah Swayne, a passenger on the return flight, as saying the boy didn't seem to be fazed by the fuss he had caused.
"He just sat there chatting away about how he'd been trying to run away from home," Swayne was quoted as saying. "He seemed quite innocent, really, and I don't think it had sunk in how serious the situation was."
The newspaper said the boy had run away from his mother while they were shopping and then made his way to the airport two miles (3 kilometers) away.
Airport officials described the boy as big for his age and on CCTV footage he appeared confident and betrayed no nervousness as he moved through the terminal.
Jet2.com issued a statement saying it had launched "a full investigation into what is a serious incident."
Jet2.com, owned by Dart Group PLC, is a European budget airline which operates 188 routes to 53 destinations. The airline traces its origins to a company founded in 1971 to fly flowers from Guernsey to the U.K. mainland.