A 15-year-old Santa Clara boy who stowed away in the wheel well of a plane from San Jose on Sunday may have hoped to hop a flight to Africa to visit his mother, but he was lucky to have survived what ended up being a much shorter trip to Hawaii.

The boy, who has not been identified, most likely survived the high-altitude flight - enduring extremely low temperatures and oxygen levels - because his body quickly went into a hibernation-like state, said doctors who have studied the effects of hypothermia and low oxygen.

"What happens is the body's entire metabolism slows down when you chill the body that low," said Dr. Tom Dailey, chief of pulmonary medicine at Kaiser Permanente Santa Clara Medical Center. "Obviously there's a point where you can go too far and people freeze to death. With this kid, it likely decreased the metabolism so he could survive with this very low oxygen level.

"Somehow he managed to walk that tightrope," Dailey said. "That is one fortunate kid."

Reportedly missed mother

The boy, a student at Santa Clara High School, was unhappy living with his father, stepmother and siblings and wanted to reunite with his mother and other relatives in his native Africa, Hawaii News Now reported, citing unidentified sources in the Maui Police Department.

The boy apparently picked the first plane he saw, not realizing where it would take him, authorities said.

There are dozens of accounts of people climbing into the wheel wells of planes, but only about 1 in 4 of the stowaways survives, according to the Federal Aviation Administration. It's difficult to keep track of the total number of stowaways because some might fall out of planes without anyone knowing they were there. Others may survive the trip and leave the plane undetected.

In the recent case, the Santa Clara boy most likely became unconscious only minutes into the five-hour, 2,400-mile flight, doctors said. The Boeing 767 reached an elevation of about 38,000 feet, where temperatures would have been about 50 to 80 degrees below zero.

The amount of oxygen in the air at that elevation isn't remarkably lower than at sea level, but the air pressure is vastly decreased, and that makes it more difficult for the lungs to deliver oxygen throughout the body. The heart and brain are especially vulnerable to oxygen deprivation, or hypoxia.

But doctors have long known that hypothermia, while deadly in many situations, can protect the body in low-oxygen events - such as falls into freezing-cold waters - by slowing down the metabolism. Now, many hospitals purposely put patients into a hypothermic state after a heart attack or other oxygen-depriving situations to protect their brains and other organs from damage.

"Hypothermia can be protective until the point that you die from it. It puts you in a metabolic icebox," said Dr. Paul Auerbach, a professor in emergency medicine at Stanford University who has written two medical survival books: "Wilderness Medicine" and "Medicine for the Outdoors."

Possible complications

"Is it a miracle that he survived? I guess it depends on your definition of miracle," Auerbach said. "The odds are against you, though. It's not something I would recommend anybody try."

Doctors added that there can be lasting complications from either hypothermia or hypoxia, or the combination. People can suffer frostbite, for example, or brain damage that might not be immediately detectable.

The boy was found wandering and conscious around the tarmac in Maui about an hour after the flight landed, authorities said.

He is "resting comfortably at a local hospital," Kayla Rosenfeld, spokeswoman for Hawaii's Department of Human Services, said Tuesday. "Child Welfare Services officials continue to work with the appropriate agencies to ensure the youth's safe return to his home in California."

Authorities said the boy scaled a fence at Mineta San Jose International Airport in the predawn hours Sunday, then clambered up the landing gear of the passenger jet without anyone noticing.

He is not facing criminal charges in Hawaii or in San Jose and was released to social workers, authorities said.

Marvin Moniz, district manager for the Kahului Airport in Maui, said the boy told investigators that he wanted to visit his mother, whom he had not seen for several years.

"He spoke fairly good English and spoke fairly slowly. He was soft-spoken. He appeared to be tired, a little weak," said Moniz, who had offered the boy some Maui-style teriyaki meatballs, rice, a bag of cookies and a bottle of water.

Moniz said he saw surveillance video showing the boy's legs dangling from the wheel well of the plane before he dropped down to the tarmac. The boy said he got onto the closest plane he saw in San Jose.

"I asked him, 'Did you know you were coming to Hawaii?' and he said no," Moniz said. "He had no idea.

"I've never seen anything like it," he said. "I think he beat all the odds. If I went to Vegas, I would take him with me."

The boy's family in Santa Clara has declined to speak to reporters. They live in a one-story home on Forbes Avenue east of the San Tomas Expressway. It was unclear Tuesday whether any relatives were in Maui, or on their way, to be with the teen.

School reaction

At Santa Clara High, Principal Gregory Shelby declined to discuss the teen in detail, citing confidentiality concerns. But he said, "Our district would be ready to have him back."

The incident has raised questions about whether the San Jose airport's perimeter security is adequate. Airport spokeswoman Rosemary Barnes said the airport "meets and exceeds" all federal requirements but acknowledged that the boy eluded detection because he hopped over a fence "under cover of darkness."

Erin Allday and Henry K. Lee are San Francisco Chronicle staff writers. E-mail: eallday@sfchronicle.com, hlee@sfchronicle.com Twitter: @erinallday, @henryklee