It wasn't just luck that saved all but two of the 307 passengers aboard Asiana Airlines Flight 214, aviation safety experts said Monday. 
 
 It also took Federal Aviation Administration mandates from the late 1980s that forced manufacturers to bolster seat strength to withstand traumatic force and to line cabins with fire-resistant materials to stall fires. 
 
 "If this had happened before then," said Michael Barr, a senior instructor at the Aviation Safety School at the University of Southern California, "the inside of that plane would have looked like a jigsaw puzzle dropped from a second-floor window." 
 
 Instead, photos released by the National Transportation Safety Board show that rows of seats inside the Boeing 777 remained mostly intact, which allowed passengers to unbuckle and flee toward emergency exits. 
 
 The fire that followed may have been delayed just long enough to give crew members and rescue workers time to evacuate those who were stuck, Barr said. 
 
 A few seconds count 
 
 "A few seconds here and there adds up," he said. "It's the difference between saving lives." 
 
 Flight 214 clipped a seawall, skidded, briefly went airborne again and finally slammed to earth on its belly. The fact that most passengers survived may be due to a seat-strength upgrade that federal regulators required on new passenger planes starting in 1988, said Todd Curtis, an airline safety expert and creator of the website AirSafe.com. 
 
 Before then, seats were designed to absorb nine times the force of gravity, or 9 g's. But Curtis said crash investigations often revealed that passengers could have survived the impact if their seats had not uprooted and launched them into cabin walls. 
 
 Sometimes those seats blocked escape routes for surviving passengers, who then died as fire engulfed the plane. 
 
 Now, all passenger airlines are required to install seats that can absorb 16 g's. 
 
 Curtis said the crash of Flight 214 appears to have borne out the value of the strengthened seats. 
 
 "You see the cabin floor buckled, but the seats did not come unglued," he said. "It prevented more people from being killed or injured. If those seats come undone, it's just chaos in there." 
 
 About 30 years ago, regulators started requiring airlines to outfit planes with fire-resistant materials, which increases available evacuation time, Curtis said. Even blankets and pillowcases must be made of special material. 
 
 Better training 
 
 Curtis also pointed to improved airline training that emphasizes clearing a crashed plane within 90 seconds. Crews are run through a variety of scenarios, including some in which multiple escape routes are blocked. 
 
 Federal investigators said Monday that two of the inflatable slides on Flight 214 deployed inside the aircraft. Crew members had to take axes to at least one to free a trapped colleague. 
 
 Photos showed a detached engine blocked at least one of the remaining exits. 
 
 "It looks like they only had one-fourth of their emergency exits to work with," Curtis said, "and they still managed to get everyone off." 
 
 Another safety expert said the crew's actions, firefighters' rapid response and the lack of panic among Flight 214's passengers were also factors in the minimal loss of life. 
 
 "When the plane lands and the tail pops off, there's not a lot a manufacturer can do to prepare for that scenario," said John Silcott, an airline pilot and executive vice president of Expert Aviation Consulting in Indianapolis. "At that point, there's nothing a pilot or anyone can do. It's not like you could design and push a button and make it stop." ||||| Many of those hurt in the crash of Asiana Airlines Flight 214 on Saturday have spinal injuries, according to a doctor who treated them — and they’ll likely need long-term treatment. 
 
 
 
 Patients have fractured spines, stretched ligaments and head injuries, said Dr. Geoff Manley, vice chairman of neurological surgery at the University of California San Francisco. The pattern of injuries is surprisingly similar, he told NBC News, and paints a picture of people badly bounced around as the plane hit short of the runway and tumbled. 
 
 “There was some blunt force injury from seatbelts and people striking their heads against the seat and armrests,” Manley, who treated many of the patients at San Francisco General Hospital, said in a telephone interview. 
 
 “We have a lot of spine trauma.” People’s spinal cords were fractured and hyper-extended, meaning they’ll need to be kept stable so the spinal cord itself isn’t damaged any more. 
 
 “There are some people very, very badly hurt.” San Francisco General treated 53 patients, 34 of whom have been discharged. Hospital officials said six of the patients there were in critical condition. 
 
 "These injuries include large abdominal injuries, spine fractures, head traumas, and orthopedic injuries," Dr. Margaret Knudson, chief of surgery at the hospital, told a news conference. 
 
 Some of the worst injuries are traumatic brain injury, Manley added. Some passengers also suffered internal injuries from being flung against their seat belts. “They were all in the same type of seats, and they all had their seat belts on,” he said. So many of the injured have the same types of spinal damage. 
 
 There were 291 passengers and 16 crew members aboard the flight, which had crossed the Pacific from Shanghai with a stop in Seoul before crashing as the pilots were attempting to land. More than 180 people were transported to San Francisco area hospitals, officials said. 
 
 Injuries range from bruises and minor burns to bone fractures, head and internal injuries. Officials said 49 of the patients were seriously injured. 
 
 Two people, both teenage girls, were killed in the crash, but Manley noted that he had expected more serious injuries. 
 
 “Given the nature of the accident, it is remarkable we did not see more significant injuries,” he said. 
 
 As the plane hit the ground, passengers would have been thrust forward, backward, up and down. “This is whiplash to the nth degree,” Manley said. “People were being flipped forward and back as the plane crashed. When you bend forward or backward like that, you can literally crush (the vertebrae).” 
 
 In some of the passengers the spinous process – the piece of bone you can feel when you touch the back of your neck – cracked in half. 
 
 One patient appears to be paralyzed from the waist down, Manley said, although it’s early to tell. 
 
 Even those with no obvious fractures are in danger of becoming paralyzed, as stretched ligaments can no longer keep the spine stable. 
 
 “We have a number of these injuries that are highly unstable,” Manley said. “We are going to go in today and put screws and rods and things like that and stabilize the spine.” 
 
 Knudson said two patients in critical condition had "road rash" injures that suggested they were dragged along the ground. "We don't know how they got it but we were a little surprised to see it," she told a news conference. 
 
 “We’ve got some very minor burn injuries which went along with the road rash but we did not see burn injuries," Knudson added. “We do have one patient who has (smoke) inhalation injuries.” Knudson said many patients had crush-type injuries, perhaps from heavy items falling on them. 
 
 Emergency workers who grabbed and stabilized passengers on the runway undoubtedly prevented worse injuries, he said. 
 
 
 
 “Obviously, people needed to jump off that plane because it caught on fire,” Manley said. But immediate triage meant patients with the worst injuries, especially head injuries and damage to internal organs, went straight to hospitals, while others were put in back boards or fitted with cervical collars to prevent more injury to their spinal cords before they were sent. 
 
 Knudson agreed. “I can tell you two of them likely would not have survived" without it, she said. 
 
 While many children were aboard the plane and have been treated, many appear to have escaped the severe kinds of spinal injuries seen in the adults, Manley says. “Most of the severe injuries were in adults,” he said. 
 
 "We don't have too many severely injured children," Knudson agreed. 
 
 “I think kids are typically more flexible,” Manley said. “They have a lower center of gravity. Little kids are made to rough and tumble. They do weather injuries well.” 
 
 Spokespeople at several Bay Area hospitals said they had treated and released lightly injured patients. Stanford Hospital treated 55 patients, with two in critical condition; California-Pacific Medical Center is treating nine patients and released five, the University of California San Francisco has treated and released 15; Kaiser Permanente treated and released 15 from two of its area hospitals; St. Mary's Medical Center admitted four patients while the associated St Francis Medical Center treated seven and has released six of them. 
 
 Matthew DeLuca, Ami Schmitz and Stacey Naggiar contributed to this story.
– If Saturday's plane crash in San Francisco had happened 25 years ago—or if passengers hadn't been wearing seat belts—the death toll would have been a lot higher than two out of the 307 passengers and crew, experts say. FAA mandates in the late 1980s forced manufacturers to bolster seat strength, and if this had happened before then, "the inside of that plane would have looked like a jigsaw puzzle dropped from a second-floor window," an aviation safety expert tells the San Francisco Chronicle. Among the survivors, there are numerous spinal injuries that are the result of being violently shaken in their seats, says the doctor overseeing the passengers' care. "They were all in the same type of seats, and they all had their seat belts on," so many of the injured have the same pattern of spinal damage caused by their upper bodies being flung over their lap belts, Dr. Geoffrey Manley, the neurosurgery chief at San Francisco General Hospital, tells NBC News. Other experts say the injuries are like those before shoulder belts in cars, though it's not clear whether shoulder belts in planes could have prevented the injuries, the AP notes. Six patients are still in critical condition and two are unable to move their legs, though Manley says remarkably few of the many children on the flight are among the seriously injured. "They have a lower center of gravity. Little kids are made to rough and tumble," he says. "They do weather injuries well."