Passed five checkpoints without being stopped
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-kilometre) 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 yesterday.
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.
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.
five security checks passed
"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 traveller has a boarding card or a staff pass.
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.
A newspaper report said the boy had run away from his mother while they were shopping and then made his way to the airport two miles (3 kilometres) away.
Jet2.com issued a statement saying it had launched "a full investigation into what is a serious incident".