Mr McKinley already faces traffic and bad cheque charges

Shipping clerk Charles D McKinley, 25, was only discovered when he arrived on the doorstep of his parents' home in the town of DeSoto.

Transport officials are investigating the case amid heightened concern that cargo flights are a continuing weak spot in US airport security after 11 September.

Mr McKinley was arrested in Texas for unrelated previous offences but may also now face charges of stowing away.

CARGO CLASS Wooden crate measured 106 cm by 91 by 38; Mr McKinley is 1.7 metres tall Journey took 15 hours during which Mr McKinley reportedly had neither food nor water Mr McKinley left the crate several times en route to stretch his legs

Speaking from his cell, he told local TV he had been feeling homesick and a friend suggested he could save money by flying as cargo.

Billing the $550 freight charge to his employer, he climbed into the crate and managed to travel the journey undetected until a deliveryman witnessed his emergence at the other end and called the police.

"I'm sitting there thinking, 'Oh God, I don't know why I'm doing this'," he recalled.

"I'm sitting there thinking like any minute somebody will notice that there's somebody sitting inside this crate. ...No one did."

High-risk ruse

The federal Transportation Security Administration (TSA) has interviewed Mr McKinley twice to learn how he got past security.

"We're not aware this has happened previously, so obviously it's something we are investigating aggressively," said a TSA spokeswoman, Suzanne Luber.

Air cargo planes are believed to receive less attention than passenger planes because of the sheer volume of freight passing through.

"There are millions of shipments around this country whether it be a cargo container or a rig or shipping coming into our ports and the fact of the matter is you cannot open and examine every one of those," said FBI Director Robert Mueller.

Pilot Air Freight, the company which carried the unusual cargo, pointed out that, apart from anything else, Mr McKinley had narrowly escaped death by having the good fortune to fly in pressurised, heated cabins.

"He could easily have died," said Richard G Phillips, the company's chief executive.

And, despite the risks and discomfort, it wasn't even any cheaper for Mr McKinley to travel in a box.

For $550, "he could have flown first-class," Mr Phillips said.