(CNN) -- The first sign something was off was when the ground crew at Kahului Airport in Maui noticed a boy wandering the tarmac, dazed and confused.
The story he told officials was even more incredible.
The 16-year-old apparently hitched a ride from San Jose, California, to Maui, Hawaii, in the landing gear wheel well of a Boeing 767, Hawaiian Airlines said Sunday.
"Our primary concern now is for the well-being of the boy, who is exceptionally lucky to have survived," the airline said.
He certainly is.
If his story pans out -- and the FBI has been called in to investigate -- he rode in the tiny cramped compartment for almost five hours, at altitudes that reached 38,000 feet, without oxygen and under sub-zero temperatures.
That has some experts questioning his story.
"The odds of a person surviving that long of a flight at that altitude are very remote, actually," airline analyst Peter Forman told CNN affiliate KHON. "I mean, you are talking about altitudes that are well above the altitude of Mt. Everest. And temperatures that can reach 40 degrees below zero.
"For somebody to survive multiple hours with that lack of oxygen and that cold is just miraculous. I've never heard of anything like that before."
Still, several parts of the boy's story pans out.
Authorities don't know who the boy is. He didn't have an ID. The only thing he did have on him was a comb.
He told authorities he was from Santa Clara and ran away from home Sunday morning, said FBI Special Agent Tom Simon.
Investigators have surveillance camera footage of him hopping the fence at San Jose International Airport.
There's also camera footage of him walking across the ramp in San Jose toward the Hawaiian aircraft, the California airport said.
He told investigators he crawled into the wheel well of the plane, and lost consciousness when the plane took off.
An hour after the plane landed at Kahului Airport, the boy regained consciousness and emerged to a "dumbfounded" ground crew, Simon said.
The Maui airport has video of him crawling out of the left main gear area.
"It makes no sense to me," Simon said. "I understand your skepticism."
He hasn't been charged with a federal crime, and was placed with child protective services.
There have been other instances of stowaways on wheel wells -- but they haven't ended well.
In February, crews at Dulles International Airport in suburban Washington found the body of a man inside the landing gear wheel well of an Airbus A340 operated by South African Airways.
In 2010, a 16-year-old boy died after he fell out of the wheel well of a US Airways flight that was landing at Boston Logan International Airport.