Transcript for Men Scale Bolivian Mountain, Find Black Box Remains From Crashed Flight 980
Tonight we bring you an extraordinary adventure courtesy of two young men who read on the internet about a mysterious plane crash from more than three decades ago and decided to try and solve it. Here's ABC's David Kerley. Reporter: On this remote Bolivian peak -- That's where we're getting to. Reporter: -- Two American adventurers -- Say what up. Reporter: -- With no mountaineering experience -- This is worse. This is much worse. Reporter: -- Are hoping to solve a more than 30-year-old mystery. To me that looks impassable. Physically really, really demanding. Reporter: And wait until you hear how they got here. We went to Boston to meet Dan Futrell and Isaac stoner, who guys who one day searching the internet found this wick piedia page, a page revealing that just 19 aircraft black boxes worldwide are unaccounted for, including one on Bolivia's 21,000-foot mount illimani. Never recovered, it said, because of inaccessible terrain. So you find this by googling and decide what? We can go find this black box that nobody's found for decades? Well, Dan had to talk me into it, which took a little while. Like come on, people have been to the moon, people have been to the top of Everest, what does inaccessible mean? And with a couple of Google maps and a few videos we thought we can do it. Trying to reach that eastern airlines jet which crashed into the side of a mountain outside La Paz. A Boeing 727 with 29 on board including eight Americans slammed into mt. Illimani new year's day 1985. The full-scale investigation by inspectors from the national transportation safety board is now under way. Reporter: But the crash site, so remote and at 19,000 feet above sea level so high that those investigators couldn't get to the site. Tom howder, who had just joined the NTSB, says a team was sent back -- They got to the accident site, but by then the area was covered in like 30, 40 feet of snow. So they found a few parts but nothing definitive. Certainly they didn't find the recorders at that time. And essentially, the investigation came to a halt. Reporter: Leaving a mystery. Was it a navigational error or something more sinister? There are plenty of conspiracy theories. It was known that drugs and things were found on air flights. There was the wife of the ambassador to Paraguay on board. What really happened here? The only way to know is to get to that tape. Reporter: So flight 980 was added to the list of those handful of crashes around the world where the black boxes were never recovered. For the relatives of those lost on board a fact that was hard to bear. My dad, mark Lewis berg, he was the flight engineer on eastern airlines flight 980. Stacy Greer was just 3 years old when her dad didn't return from the South American flight. My mom never really talked about it. I just always knew that I was missing my dad. Did you ask yourself through the years, I wonder what really happened to my dad? Yeah. Yeah. Reporter: Which brings us back to those two American adventurers from Boston. How do we stay alive? We can either find the black box or not. He's got my back. Reporter: Who were looking for their next challenge. Are you guys both mountaineers? No. Not even close. We haven't done anything near what real mountaineers would call mountaineering. Reporter: To prepare they rented an altitude tent, sleeping in it for a month to acclimatize. They ran stairs at Harvard's stadium. And went to an outdoor store to buy some climbing gear. Was it the sense of the adventure? Was it the mystery that appealed to you? I think a little bit of both. Maybe we could succeed where all these other expeditions not managed to. Second wind. Pete? Remarkably composed. Second wind. Reporter: With just three hours of training from their guide -- Around the corner there and we just can't do it. Reporter: -- They headed up the mountain. Drop packs. This is a good place. Reporter: And then found what they were looking for. We immediately found pieces of the plane. And that's the first time where it was kind of real. Reporter: But over all those years the wreckage had slid down the mountain and spread out a lot. The debris field was much, much larger than we had anticipated. Reporter: They are now looking for the proverbial needle in a haystack, the black boxes in a massive rock field. It did seem like the goal of finding the flight recorders might be completely impossible. Found this thing. Which is the right color but cracked open like an egg. Piece of Orange metal. I flipped it over and it was very clearly international Orange. But it's really bent up. I expected the black box to be intact, and I also found some magnetic tape. Promising. But not until the last day of their trek at 16,000 feet, the sun going down, does Isaac finally make the discovery that they had flown to Bolivia and climbed this mountain to find. And so I just flipped over a piece that I hadn't flipped over before, and it had a little wrap on this bundle of wires that said ckptvorcdr. We were standing there on this beautiful mountainside holding this thing that we'd come a long way to find, that people had claimed to be stolen or hidden, and there it was. There it was. They came back down and called me and told me what they had found. Time just froze. Reporter: Mystery solved, right? Hand over the tape to the NTSB and see what's learned? Wrong. Bolivian and U.S. Relations are strained and the Bolivians, even after all these years, are in charge of the investigation. E-mails from Boston and certified letters from ABC news sent to the Bolivian embassy went unanswered. A standoff while the box and possible remnants of the recording tape are sitting on a Boston kitchen counter. Wait a minute. This is like a cardboard box. Basically, the black box is living in your apartment. Yeah. What you see here are six different pieces. This one here is the piece that Isaac -- the last piece that he found. It is this the eureka. This is when you think you know you've got it. This is krornt Vo recorder. But inside a plastic froozer bag -- The good stuff is this -- This stuff right here. Reporter: That is a partial spool of what appears to be magnetic tape. A possible recording. Is it unusual that eyre able to go find a black box. It's unusual that now it's seemingly our task to convince the country of Bolivia to cooperate with the country of the United States. Reporter: Just in the past two weeks, progress. The Bolivians now saying they're willing to allow the NTSB to examine the tape. But who gets any information gleaned? That's not been determined. So the box sits. Stacy Greer got something she wanted. A piece of the plane that her father died on, which she now wears around her neck. Do you think you'll ever get an answer as to what happened to your dad? I hope. Does it solve the mystery? Maybe it does, maybe it doesn't. At least what we should be able to say is that we have a thing now that might have an answer, we need to be able to check the box that either yes or no it does or doesn't. Reporter: A mystery sitting in a cardboard box on a kitsch encounter. For "Nightline" in Boston I'm David Kerley.
This transcript has been automatically generated and may not be 100% accurate.