34,000 feet over the skies of arizona last evening. when a large hole ripped open atop a southwest airlines jet full of passengers. the oxygen mask we hear about on those routine preflight safety announcements became life safers to passengers. the interior of the plane was exposed to open daylight. dozens of the airline's 737s are grounded, temporarily taken out of service by southwest itself. and invest gators are racing to learn what happened and whether there may be a larger maintenance problem with the fleet. tom costello is in our washington bureau now with more. >> reporter: lester, nearly 80 southwest 737s have been taken out of service as southwest looks for any signs of the kind of cracking that may have caused this hole to open up midnight. 118 passengers on board along with five crew members. they all got off alive, one flight attendant and a few passengers passed out from a lack of oxygen as air was sucked out of the cabin. investigators on the ground in yuma, arizona today looking over the southwest 737 that made an emergency landing late friday, after a five-foot hole ripped off midnight. passengers described a loud bang, then a rush of heiress caping from the cabin. >> and bam, i mean, just incredible noise, and then while you're trying to process what just happened, then oxygen masks come down. >> not everyone was getting their mask on. some were having problems, people were passing out. it was not good. >> reporter: flight 812 had just approached flying altitude, when a large portion of the skin r ripped open, right over the passengers heads. the pilot quickly descended then made an emergency landing at a military base in yuma. >> i thought we were going down, i really did. >> any time you have a rapid decompression of an aircraft is a big deal, just from the standpoint of safety. it is a startling event not only for the passengers, but the flight crew. >> reporter: the plane involved, a 15-year-old 737 300. another southwest plane had a hole open up in the roof nearly two years ago, forcing an emergency landing in west virginia. airlines were ordered to inspect 737s for signs of metal fatigue. two years ago, the faa find southwest $7.5 million for failing to conduct timely crack inspections on its 737 fleet. we talked to the ntsb on the scene. >> we will be looking at everything. right now we are here to look at this accident, and if we find issues related to this accident that could be applied to the rest of the fleet, we will make that point known. >> reporter: and metal fatigue has led to tragedy. in 2005, a chalk's airways plane crashed on takeoff from miami when its wing ripped off. in 1988 the top of an aloha airlines plane tore off in flight. a flight attendant was sucked out of the plane to her death. metal fatigue is caused by the constant movement of an airplane, the constant contraction and expansion. this aircraft was 15 years old, with nearly 40,000 cycles. >> as you know, there are an awful lot of 737s in the sky, a lot of them doing a lot of short hops, takeoffs and landings as you described. what's the word on the airplane right now. >> this is a workhorse for the industry, as you well know, but it is aging. southwest has been trying to remove or get rid of the 7 737 300s and replace them. the faa says in the united states right now, there are a total of about 288 737-300s in service worldwide, about 1,000. >> tom costello in washington, thank you. greg fife is a former ntsb investigator, he joins us from denver. i think a lot of people are looking at this, a three-foot hole in an airplane, how much danger were these passengers in? could this plane have crashed? >> no, not from the standpoint of this type of failure in the fuselage itself. the big thing is, if there was a structural compromise where -- like aloha where you lost a very big chunk of that airplane. in this case it ripped off a three to four foot hole. there's tear straps under the skin to prevent that rip from propagating even further. from that standpoint they were never in danger of crashing this airplane. >> we have seen these incidents before. has the industry underestimated the toll that age and repeated landings and takeoffs take on airplanes? >> i don't think they've underestimated it, lester, i think we have to be very cautious, because we know from history, there's been aging aircraft issues and, of course, this is an older aircraft. we have to look at the fact that this is a new event the. it could be something totally unrelated to the process of aging aircraft, but more to the inspection now. there are comprehensive inexpectations and they could induce damage, the mechanics could induce damage by doing some of these inspections. we have to wait until the ntsb does its investigation. >> at 34,000 feet, you have to get oxygen on in a hurry or as we saw on that flight, people start passing out. >> i think security now is more highlighted than safety with regard to -- these are rare events as far as a rapid decompression or explosive decompression. i think from the standpoint of security, they're more concerned about the bad guys doing something bad in a laboratory, with an oxygen generator as we've seen, the damage that can be done from valujet. i think if there is an event like this, whoever is in a lavatory at the time, will have to find their way to an oxygen mask. i think the odds are against somebody being compromised as far as their health is concerned without a lavatory oxygen generator. >> thanks for sharing your expertise with us. there were two other air scares in the past 24 hours, a delta flight from atlanta landed safely in little rock after hitting a flock of birds. now, to libya. a friendly fire accident that has left a dozen rebel fires dead. a nato air strike targeted the forces fighting against moammar gadhafi. this as the u.s. is ending combat strikes in libya. richard engel has the latest for us from benghazi. >> reporter: this was the deadliest case of friendly fire in this conflict so far. but it has not created a major backlash, an angry reaction, as rebel leaders realize that they still need western air support. the rebels front line is slowly advancing through the desert near the town of bregga. nato air strikes clear the way. targeting gadhafi's tanks and jeeps. jeeps that look just like the ones used by the rebels. friendly fire on this chaotic highway battlefield may have just been a matter of time. witnesses say a nato jet today destroyed a convoy of vehicles killing at least a dozen rebels. but the rebels may have triggered it. witnesses say the rebels who have a tendency to shoot wildly in the air, fired anti-aircraft guns at the nato aircraft which shot back. the rebels quickly buried their dead in makeshift graves nearby. the opposition leadership in benghazi called the incident unfortunate, but did not condemn nato. >> we feel sorry for the families who lost their children in this particular attack, however, we think it is necessary for nato to keep doing what they are doing, because the benefit is much greater than what happened today. >> nato says its investigating the attack, which comes as the united states is preparing to end its combat missions over libya. the pentagon has said, as of sunday, american aircraft will continue to gather intelligence and refuel fighter jets, but no longer drop bombs. it ends a critical phase of the combat operation. and avoids the risk that american troops will cause civilian casualties, always a significant danger in an air campaign without troops on the ground to identify targets. as of now here in libya, the deadline for u.s. aircraft to stop flying bombing missions has passed. however, u.s. planes will remain on stand by in case they're called for for emergency supports. >> richard engel in benghazi, thanks. turning to afghanistan and another day of deadly protests. peter alexander reports on the latest upheavals in a country where americans continue to serve and die. >> reporter: in the southern city of khandahar, thousands of protesters stormed the streets today, unleashing a second day of deadly riots. the demonstrations fuelled by the burning of a koran, by american terry jones, the radical pastor of a fundamentalist church in florida. who sparked worldwide condemnation after threatening to do the same last september. the violence started friday, where protesters killed seven foreigners at a united nations compound. it comes just three months before the americans are scheduled to begin handing over security to afghan troops. a process set to begin this july and end in 2014. >> in many places in afghanistan, security is much better, but in a lot of the critical areas, the challenge is huge and we're not going to make any improvement between now and the time we're going to leave. >> most attention has been focused on america's intervention in libya as well as japan. 100,000 troops are system fighting in afghanistan, where the dangers have not diminished. since the war began, 1,410 american service members have lost their lives in afghanistan. 75 service members this year alone. on thursday, six flag draped coffins arrived at dover air force place. the fallen all members of the 101st airborne division screaming eagles, suffering its deadly tour since vietnam. among those lost, frank adamski of connecticut, home just last month to celebrate his daughter's first birthday. and jeremy faulkner of georgiaing who was due home this month. >> i know he would want us to think he died for the right causes. and that's the idea that i have, that he didn't die in vain. >> reporter: nearly ten years into america's longest war, the sacrifice endures. peter alexander, nbc news, new york. as many as 1,000 people may be dead in the power struggle that is tearing apart the west african nation of ivory coast. a roman catholic charity and international red cross are reporting the killings which took place in a town where thousands of u.n. peacekeepers are stationed. they held elections last november, the president was defeated but is refusing to give up power. forces loyal to the candidate who won the election are trying to oust him. deadly violence today in northern ireland. a young catholic policeman was killed when a bomb exploded under his car. police blame ira dissidents. an ira splinter group detonated a car bomb that killed 29 people and injured hundreds of others in a previous attack. back here at home, president obama had a busy saturday placing calls to house speaker john boehner and senate majority leader harry reid pressing them to agree on a $73 billion series of cuts from this year's budget. the government faces a shutdown on friday, without a budget settlement or another extension of the deadline. meanwhile, the president's political advisers say he could file with the federal election commission as early as monday and begin raising money for his re-election campaign. but those same advisers say that could be delayed until the budget impasse is resolved. david gregory will have much more on this tomorrow morning on "meet the press." senator dick durbin of illinois will be among david's guests. still ahead this saturday night on "nightly news" troubling news from japan. investigators discover a source of radiation from the damaged nuclear plant leaking directly into the ocean. where's spring? from a major league hail storm in washington to a heat wave in the west. and tonight, forecast for dangerous weather tomorrow. hoop dreams, getting a hometown hero's family to the big game. when your eyes are smiling... you're smiling. and when they're laughing... you're laughing. be kind to your eyes... with transitions lenses. transitions adapt to changing light so you see your whole day comfortably... and conveniently while protecting your eyes from the sun. ask your eyecare professional which transitions lenses are right for you. 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[ female announcer ] ask the doctor about your loved one trying the exelon patch. visit exelonpatch.com to learn more. another setback to report tonight in the effort to gain control of the fukushima nuclear power plant in japan. highly radioactive water continues to leak directly into the pacific ocean. officials now know where it's coming from. lee cowan is in tokyo tonight. >> reporter: they are the latest images from the crippled power plant. steam and smoke can still be seen rising from reactor number four. but it is reactor number two that is the most immediate concern. japan's nuclear regulator say highly radioactive water flooded that compartment and it was seeping out of a crack. engineers hope to seal the leak, but since there is so much water, so far, that hasn't worked. the radioactive iodine will disperse quickly once it hits the ocean. the real threat is to the workers on site who still have to battle to stop it. today japan's prime minister arrived in the disaster zone. the first time he set foot in the devastated landscape since this tsunami roared ashore three weeks ago and the view is devastating. there are so many bodies being recovered, 12,000 at last count that identification is almost impossible. local crematoriums are either destroyed or overloaded. some bodies are being shipped to tokyo's crematorium, where buddhist monks now gather to offer blessings for those they've never met. >> we want to be with them, those who lost their loved ones. >> reporter: more than 20 bodies a day have been coming here. outnumbered only by those who come to pay their respects. they arrive every few minutes, strangers bringing flowers and ernest offerings to 240those wh have lost so much. their bodies, this woman lamented, are just so far from home. out of all that is lost, and there is plenty. dignity, it seems, still stood strong. lee cowan, nbc news, tokyo. when we come back, what's behind all the wild weather this weekend. and there's more on the way. with an irregular heartbeat called atrial fibrillation, or afib? if so, now's the time to talk to your doctor again, even if you're already taking medication to reduce your stroke risk. atrial fibrillation can cause a blood clot to form here, in your heart, that can break free and go straight to your brain, where it can cause a serious stroke. strokes that are twice as likely to be deadly or severely disabling as other types of strokes. but if you're one of the 2 million people who have atrial fibrillation, there's never been a better time to talk to your doctor. because you and your doctor can choose from different kinds of medicines to help prevent a stroke. for a free interactive book, call 1-877-afib-stroke, or log-on to afibstroke.com. and with this valuable information in your hand, talk to your doctor. i see you're flatulent in three languages. graduated top of your gas. 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