SAN JOSE, Calif. >>  For all the tens of billions of dollars the nation has spent on screening passengers and their bags, few airports made a comparable investment to secure the airplanes.

As the case of the San Jose stowaway shows, it did not take a sophisticated plan for a 15-year-old boy to spend about seven hours in what is supposed to be a secure area of Silicon Valley’s main airport — much of it in a wheel well of the jet that took the teen to Hawaii.

“No system is foolproof,” San Jose International Airport aviation director Kim Aguirre said Wednesday. “Certainly as we learn more, if we see any gaping holes, we will work to fill them.”

Aguirre said a perimeter search found no holes in the barbed wire fence surrounding their 1,050 acre facility, and officials were waiting to finish their investigation before implementing any additional security measures.

Jennifer Dericco, a spokeswoman for the Santa Clara Unified School District, confirmed that Santa Clara High School Principal Gregory Shelby sent a note Tuesday to staff members saying the teen had been in the U.S. for about four years, speaks English as his second language and had transferred into the district just five weeks ago.

Shelby did not return calls from The Associated Press seeking comment.

Dericco said confidentiality rules kept her from confirming the teen was a student at the school.

The boy’s father drives a taxi, Aguirre said, but she didn’t know if he works at the airport.

Aviation security experts say the San Jose airport is hardly alone when it comes to weaknesses in securing its airfield. While some larger airports have invested heavily in technology that can detect intruders, others have systems that sound too many false alarms — or don’t provide enough useful information in the first place.

“I don’t think San Jose is different than 80 percent of the airports around the country” in how secure its perimeter is, said Rafi Ron, former head of security at the closely guarded airport in Tel Aviv, Israel.

Like other major airports, San Jose has dozens of security cameras that survey its restricted areas. Indeed, the FBI says cameras actually recorded the boy on the tarmac, but no one noticed until hours later — after he had survived the 5 1/2-hour flight and clambered onto the tarmac on the island of Maui.

“What happened in San Jose can happen as we speak at other airports, because nobody can watch all these monitors” that feed video from around the airport, said Ron, now CEO of the consulting firm New Age Security Solutions.

San Jose does not, evidently, have more sophisticated technology that can detect someone climbing a perimeter fence, track a trespasser with radar, or automatically alert authorities at a central post when a video camera picks up potentially suspicious activity.

Such intrusion detection systems are the best security available, though they are not foolproof. In 2012, a man whose personal watercraft ran out of fuel swam to the edge of New York’s Kennedy Airport, scaled a fence and walked about 2 miles along the airfield before being spotted.

All this despite a $100 million system of surveillance cameras and motion detectors.

The boy in San Jose told authorities he jumped a fence and climbed up the landing gear of the closest plane. Video shows him on the airfield a little after 1 a.m. Sunday, said a law enforcement official briefed on the investigation. The official was not authorized to speak publicly about the case and spoke on the condition of anonymity.

It is not clear how the teen spent all the time before the plane took off around 8 a.m. FBI spokesman Tom Simon in Honolulu, where the boy is now resting in a hospital following his harrowing journey, said the teen “literally just slept on the plane overnight.”

He has not been charged with any crime.

The fact that he survived is remarkable: At a cruising altitude of 38,000 feet, temperatures in the wheel well would have been well below zero and the air so starved of oxygen that he likely passed out. In response, his body could have entered a hibernation-like state, from which he emerged once he was back on the ground, experts say.

Unlike passenger and baggage screening, which is the domain of the U.S. Transportation Security Administration, the responsibility for protecting facilities is shared by the airport and federal and local authorities.

While technology can help spot intruders, it also can overwhelm with information.

At some airports, software monitors video feeds for potentially suspicious activity and sounds an alarm when a situation merits human attention. The problem is that many of those alarms are false.

Poorly performing systems might have 10 false alarms per camera per day, said Illy Gruber of NICE Systems, a company that provides such software to airports.

“It’s way too many alerts,” she said. As a result, they “are going to be ignored.”

Gruber said her company’s system can reduce the number of false alarms to two or three per camera per day.

A flood of false alarms is not a problem at smaller airports used by private planes. A 2011 study by the Government Accountability Office found that of 10 civil aviation airports, nine had no intrusion detection system and the 10th had a partial system.

The TSA said it has spent $80 billion on aviation security since its inception shortly after the 9/11 attacks. That does not include perimeter security.

“We were investing all our resources in the front door, which were the passengers and their bags,” said Ron, the security consultant. “And we left the back door open. And that was the perimeter and access to aircraft.”

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Pritchard reported from Los Angeles and can be reached at https://twitter.com/lalanewsman. Contributing to this report were Oskar Garcia and Audrey McAvoy in Honolulu, and Rhonda Shafner in New York.