HONOLULU (AP) — Three times in recent years, intruders got past the security fencing that surrounds Honolulu International Airport, according to an Associated Press investigation.

In 2012, airport employees found an injured 27-year-old woman lying in a culvert inside the security fence line.

In 2013, a woman entered airport property through an exit gate and a 40-year-old man said he had climbed a fence to reach the airport operations area. Authorities issued an unauthorized entry citation and took him for medical observation.

Airports say breaches are relatively rare. Security measures typically include fences, cameras and patrols, but there are gaps. Not all of the miles of fences are routinely patrolled or covered by video surveillance.

But they do happen, and not just in Honolulu.

Between January 2004 and January 2015, there have been at least 268 perimeter security breaches at 31 major U.S. airports, the AP found. Incidents ranged from fence jumpers taking shortcuts and intoxicated drivers crashing through barriers to mentally ill intruders looking to hop flights. None was terrorism-related.

Due to Hawaii’s rules for how long official documents must be kept, officials at the state Department of Transportation said they would not have records prior to 2012 if a breach did not result in a police investigation.

In a search of media reports, AP identified a fourth breach: In 2004, the Honolulu Star-Bulletin reported that a 17-year-old Hawaii Kai boy rammed his sports car through a locked airport security gate as he fled a traffic stop.

Until now, few of the incidents have been publicly reported. Most incidents nationwide involved intruders who wanted to take a shortcut, were lost, disoriented, drunk or mentally unstable but seemingly harmless. A few had knives, and another was caught with a loaded handgun.

The lapses nevertheless highlight gaps in airport security in a post-9/11 world where passengers inside terminals face rigorous screening and even unsuccessful plots — such as the would-be shoe bomber — have prompted new procedures.

“This might be the next vulnerable area for terrorists as it becomes harder to get the bomb on the plane through the checkpoint,” said airport security expert Jeff Price.

Since the Sept. 11 attacks, hundreds of millions of dollars have been spent to upgrade perimeter fencing, cameras and detection technology. Many airports have dozens of miles of fencing, but not all of that is frequently patrolled or always in view of security cameras.

Airport officials insist perimeters are secure, and that an intruder being caught is proof their systems work. They declined to outline specific measures, other than to say they have layers that include fences, cameras and patrols. Employees are required to ask for proof of security clearance if a badge is not obvious.

Authorities said it is neither financially nor physically feasible to keep all intruders out.

“There is nothing that can’t be penetrated,” said LAX Police Chief Patrick Gannon, noting that even the White House has struggled with fence jumpers.

The AP’s analysis was prompted by a breach last spring in which a 15-year-old boy climbed a fence at Mineta San Jose International Airport, hoisted himself into a jet’s wheel well and survived an almost six-hour flight to Hawaii. He had wanted to go to Africa to see his mother.

Afterward, an airport spokeswoman said breaches are more common than people realize.

Through public records requests, news archive searches and interviews, the AP created the most comprehensive public accounting of perimeter security breaches from January 2004 through January 2015 at the nation’s 30 busiest airports, plus San Jose.

Among the findings:

— At least 44 times, intruders made it to runways, taxiways or to the gate area where planes park to refuel or load passengers. In five cases, including the San Jose incident, they got onto jets.

— Seven international airports in four states accounted for more than half the breaches, although not all provided data for all years examined. San Francisco had the most, with 37. The others were in Philadelphia, Los Angeles, Las Vegas, San Jose, Miami and Tampa, Florida.

— Few airports revealed how long it took to apprehend suspects, saying this detail could show security vulnerabilities. Available information showed most arrests happened within 10 minutes. Several people went undetected for hours or never were caught.

Airports are responsible for securing perimeters, and the Transportation Security Administration reviews their security plans, conducts spot checks and can levy penalties. The agency said that from 2010 through 2014, it issued $277,155 in fines for 136 breaches.

Airports are supposed to inform the TSA of lapses, but the federal Government Accountability Office in 2009 found not all incidents were reported. In 2011, a TSA report counted 1,388 perimeter security breaches since 2001 at the 450 airports that TSA regulates.

The report isn’t publicly available, and the agency declined to comment on AP’s findings.

While many incidents were benign — two trespassers were skateboarders — other intruders posed greater dangers.

At the nation’s busiest airport, Hartsfield-Jackson in Atlanta, three different intruders reached runways — in 2007, 2012 and 2014. One was an aggravated assault suspect who came within 50 feet of a plane that had landed as he was pursued by police.

In Philadelphia, Kenneth Mazik sped onto the runway in March 2012 as a plane carrying 43 people was about to land. Air traffic controllers told 75 aircraft to circle and held 80 on the ground. He faced a rare federal prosecution, spent 16 months in prison and paid a $92,000 fine.

Among the intruders, Christopher McGrath stands out. Eight times between April 2012 and March 2013, police caught McGrath after he got over the fence at LAX on a mission to board a flight. He is now at a medical lockup in Missouri.

Security firms sold $650 million worth of fences, gates, sensors and cameras to airports in the decade following the 9/11 attacks, according to industry analyst John Hernandez, though he projects spending will drop.

Officials insist that no technology solution is foolproof. Outfit cameras with software designed to help identify intruders, and there may not be enough staff to monitor images. Airports have to weigh the potential threat of harm against the hefty cost of building elaborate defenses, experts said.

“It’s one of those issues that I think until something really bad happens, not much is going to change,” Price said.

——

Contributing to this report were Associated Press researchers Judith Ausuebel, Jennifer Farrar, Susan James, Monika Mathur, Barbara Sambriski and Rhonda Shafner; writers Ian Deitch in Jerusalem, Yuri Kageyama in Tokyo and Steve Karnowski in Minneapolis; and Interactive Editor Dan Kempton in Phoenix.