The images are terrifying: Hundreds of passengers struggling to get off a burning Boeing 777 after it crashed at the San Francisco International Airport in July.



“We are so incredibly lucky that many people made it off that plane so fast with only the exits we had available,” said Ben Levy, a crash survivor who helped frightened travelers navigate their way through the wreckage and off of the airplane.



But Levy and other survivors of Asiana Flight 214 said the evacuation took longer than it should have, partly because some of the emergency escape slides didn’t work correctly. According to the National Transportation Safety Board, two slides inflated inside the cabin pinning two flight attendants to the ground and forced other crew members to deflate the slides with axes to free them, and only two of the eight slides on board deployed outside the airplane.



“When you need them to work you expect them to work,” Levy said. “You got to ask yourself, ‘Why are they not working?’”



The NBC Bay Area Investigative Unit has discovered that the government has been concerned about the reliability of evacuation slides for decades. Federal safety reports and government databases reveal that the NTSB has recommended multiple improvements to escape slides and that the Federal Aviation Administration has collected thousands of complaints about them. NBC Bay Area also discovered that just two months before the accident at SFO, regulators issued a safety alert for slides on the same airplane model — a Boeing 777-200ER — involved in the crash.



“We’ve been dealing with evacuation slides for years,” said former FAA investigator David Soucie, who worked for the administration for nearly two decades.



Soucie pointed toward a 1999 NTSB report that found emergency evacuation systems didn’t operate as expected. The report highlighted an evacuation of a Boeing 737 in Grand Rapids, Mich., in 1996 when — similar to Asiana — a slide “fully inflated inside the cabin” blocking two emergency exits.

In a subsequent report released in 2000, the NTSB found that in seven out of 19 evacuations it studied — or 37 percent of the time — at least one slide failed to work correctly.



As a result of the NTSB findings, the safety board told federal regulators that evacuations could be improved with better inspections and more slide operation demonstrations. The board also recommended that carriers report the results of the demonstrations to the FAA for further oversight.



“In 2000, the FAA responded by saying it felt it had enough recommendations in place to make it safe already,” Soucie said.



Records show that in 2009, the NTSB deemed the FAA’s response “unacceptable,” and that the board then closed out the recommendations.



But the Investigative Unit has found that airlines have continued to report problems with evacuation slides. NASA has received 111 anonymous complaints to its Aviation Safety Reporting System database in the last seven years chronicling slide malfunctions. According to a federal database that tracks airplane maintenance problems called “Service Difficulty Reports” — from 2007 through 2012 carriers reported at least 3,315 issues with evacuation slides.



Aviation experts say those reports form the basis of federal mandates known as “Airworthiness Directives.” The FAA handed down one of its most recent directives about escape slides just two months before the Asiana accident.



On May 3, the FAA announced a directive for slides found on various Boeing 777 airplanes, including the model of the aircraft that crashed at SFO — a 777-200ER. According to the bulletin, the FAA suspects that corrosion on slide release mechanisms is preventing them from deploying. The directive states that the problem could “interfere with escape slide and raft deployment, prohibit doors from opening in armed mode and cause consequent delay and injury during evacuation of passengers and crew from the cabin in the event of an emergency.”



“Whenever the FAA issues an Airworthiness Directive like they did for the 777 here it’s always an important issue that has to be taken care of,” said Todd Curtis, aviation expert and former Boeing engineer. “Usually there is something about that aircraft model that may affect safety or may affect survivability in an accident.”



In emails to the Investigative Unit, Boeing wrote that it “made recommendations to all impacted carriers in June 2011” and that a “service bulletin went to all operators worldwide.”



Curtis says since the FAA doesn’t have jurisdiction over aircraft that aren’t registered in the United States, it is up to the Civil Aviation Authority in South Korea to ensure that their carriers abide by the terms of the U.S.-issued airworthiness directive. It is unclear if Asiana had already addressed the problem, or if the Airworthiness Directive would have made a difference in the crash at SFO.



U.S.-registered Boeing 777 airplanes have three and a half years to comply with the Airworthiness Directive, and according to Curtis, the FAA would have given a tighter deadline if passengers were in any immediate danger.



Curtis also says that airplanes have built -in backups in their emergency systems. Federal regulations state that passengers and crew must be able to get off an airplane in 90 seconds with just half of the emergency exits in working order.



“There is enough redundancy in at least the 777s where even a 30 percent failure rate would not be enough to keep the slides from deploying in a way that can get everyone off safely,” Curtis said.



More than two months after the Asiana crash at SFO, Levy is still amazed that so many passengers got off of the mangled airplane safely. With no slide to aid the evacuation near his exit, he helped people climb down pieces of debris like a stepstool to escape.



“You look at the result and you are like, ‘Oh my God. Yes. We made it out alive,’” Levy said. “It’s a miracle.”



Email tips to elyce.kirchner@nbcuni.com or theunit@nbcbayarea.com or call 888-996-TIPS (8477).