Within the tight knit community of ski mountaineers, a handful of descents stand alone in terms of sheer difficulty. In 1980, Frenchman Jean-Marc Boivin became the first person to ski down the Matterhorns treacherous east face. In 1995, Canadians Ptor Spriceniek and Troy Jungen pulled a coup on the north face of British Columbias 12,972-foot Mount Robson. And in 2012, Swedens Andreas Fransson braved the Whillans Ramp on Cerro Poincenot in Argentine Patagonia.

　　But the line considered by some ski mountaineers to be the most difficult on the planet has yet to be skied. This epic descent starts 29,035 feet above sea level—dropping in from the highest point on earth.

　　The Hornbein Couloir on the north face of Mount Everest is a 1,500-vertical-foot gully whose maw opens just 1,000 feet below the peaks summit, and then spills mercilessly onto the 5,500-foot slope beneath. The narrow gully teeters between 45 and 60 degrees in steepness, bends gently in the middle, and then narrows to about the width of a standing human body. This is how American Thomas Hornbein described it, anyway, after he became the first person to ascend it.

　　Hornbein and fellow American Willi Unsoeld climbed the couloir in 1963 as a serendipitous detour after a failed attempt on the mountain’s west ridge. Less than a dozen climbers have successfully repeated the ascent since, which Hornbein wrote about in a memoir called Everest: The West Ridge. To this day, it remains one of the most technically challenging climbing routes above 26,000 feet in the world, an altitude known as the Death Zone.

　　Has Anyone Attempted to Ski the Hornbein Couloir? A thin ribbon of white suspended from the heavens, the Hornbein Couloir poses a fantasy ski descent that only two parties have ever attempted. First was the Swiss duo of Jean Troillet and Dominique Perret in 1996, then French snowboarder Marco Siffredi in 2002. Neither group succeeded, and Siffredi died during his attempt.

　　Though the north side of Everest features several potentially skiable routes, the Hornbein Couloir is the most direct among them, draining into the Japanese Couloir below it to comprise the nearly arrow-straight, 8,000-vertical-foot North Face Direct route (sometimes called the Super Direct)—which, though seldom climbed, is where climbers sometimes establish three camps.

　　Jean Troillet used exactly none of those in 1986, when he and climbing partner Erhard Loretan made one of the few successful climbs the Hornbein, in alpine style—using no fixed ropes, porters, or supplemental oxygen, and carrying everything they needed with them in one 43-hour push from Advanced Base Camp and back.

　　The ascent is widely considered one of the greatest achievements in modern mountaineering, setting a speed record, and offering a mind-bending new perspective on the viability of going fast and light at extreme elevations. But it offered another perspective to Troillet, too.

　　He and Loretan sat on the summit alone for an hour-and-a-half, and he couldn’t help but note, “The north face was covered in perfect powder, and we told ourselves it would have made a beautiful descent.”

　　After sliding back down the entire route “on their butts” for three hours, Troillet postulated that a snowboard could be a great mountaineering tool. So he went to Canada and learned to “surf,” as he calls it, and began incorporating it into his craft.

　　Ten years later, Troillet returned to Everest with Perret and an idea to ski what would then have then been the first descent of Everest—via the Hornbein Couloir.

　　The 1996 Attempt Leaves More Questions than Answers With two cinematographers, a photographer, and a team of Sherpas to help maintain Base Camp and shuttle food by yak from a monastery at 18,000 feet, Troillet and Perret spent 76 days on the mountain, waiting out the late-summer monsoons for the perfect moment to attack the north face.

　　While the more popular south side of the mountain requires navigating the treacherous Khumbu Icefall, the north side has a much simpler approach. Its 8,000-foot face erupts from the head of the Rongbuk ice flow at 21,000 feet in one straight push to the top of the world. This allows climbers to confront it head-on from Advanced Base Camp.

　　Perret, a 1990s freeskiing phenom who is now 62, remembers making two attempts to ski the Hornbein via the North Face Direct. On the first, he told Outside, they turned around at about 23,300 feet. On the second, they bailed at 27,230 feet—near the bottom of the Hornbein. He distinctly remembers getting to peer up the daunting couloir before turning around.

　　“You’re below it and you see this little mouse-hole opening in a giant wall of cliffs,” he recalls.

　　On both attempts, Perret says, violent winds, massive snow and ice fall, and multiple avalanches made it impossible to continue. He remembers skiing back down the Japanese Couloir to return to Advanced Base Camp, with Troillet on a snowboard.

　　There are, however, no photos or video of their descent. Google Earth places the ascent elevation he claims near the top third of the couloir, and not the bottom.

　　Other accounts of the expedition offer conflicting narratives. Troillet, now 72, doesn’t recall either attempt on the Hornbein, nor having descended the Japanese Couloir. To his memory, he and Perret climbed the north ridge to about about 27,890 feet, and skied from 26,250 feet, after some down-climbing.

　　Videographer John Falkiner recalls the north ridge and the first effort on the Hornbein, but not a second, and remembers it requiring a combination of crampons and skis to descend.

　　Photographer Mark Shapiro says no significant skiing happened at all. But one photo of his that appeared in a 1996 Powder magazine article shows the team ascending the North Face Direct, to the climber’s left of the Japanese Couloir, confirming at least one attempt on the Hornbein.

　　Any definitive records are sparse, belong to the analog era, and are imprecise. First-hand memories are also nearly 30 years old by now. Troillet, for his part, made his last go at a 26,000-foot peak when he was 68 and suffered a stroke while waiting out a week’s worth of bad weather in base camp, which he says took him years to recover from.

　　In 2000, a jury of French sports journalists proclaimed Perret “the best freeride skier of the century,” partly citing his efforts on Everest.

　　The ski history of Everest’s north side since then has remained short. In 1996—the same year as Perret and Troillet’s expedition—Tyrolean ski-alpinist Hans Kamerlander also ascended the mountain’s north ridge, skiing back down from 28,030 feet. He isn’t believed to have completed the whole descent on skis, however.

　　In 1997, Troillet returned without Perret, and managed to snowboard the north ridge uninterrupted from roughly 28,540 feet—650 feet higher than where he and Perret had made it.

　　Jump to 2001, and 22-year-old Siffredi pulled off the first and only complete descent of the mountain’s north side, solo, via the Norton Couloir, a wide gulley perpendicular to the Hornbein Couloir, guarded by massive seracs. It marked the second-ever complete descent of Everest, after Slovenian Davo Karničar skied the first complete descent of the south side in 2000.

　　Siffredi returned in the fall of 2002, with a notion to snowboard the Hornbein. He climbed the north ridge once again, but this time tried to ride down the convex hanging slope from the summit to the entrance of the couloir: a needle in a haystack of deadly cliffs, according to Perret. Siffredi was last seen somewhere around 28,000 feet. He was 23 at the time of his death, and his body has never been found.

　　Though the south side of Everest has been skied many times now, Siffredi’s track remains the last one down the north side, and the Hornbein remains—to the best of anyone’s knowledge—unskied and unridden.

　　Red Tape and Bottled Oxygen Despite the failed attempts, Troillet still believes the Hornbein Couloir can be skied.

　　“If there’s enough snow, it goes, but it might take one rappel,” he figures. “And then to do it in proper style you would ski the Japanese Couloir after, which can have really great snow in it. It did when we were there in 1986, and it would have made for great snowboarding.”

　　Enough snow to fill in the Hornbein, but not wipe out the face below it, is the formula that Troillet describes. But therein lies the rub, since too much snow is exactly what turned Troillet and Perret around in 1996, according to Perret.

　　The Himalayan monsoon season ends in late September, leaving the mountains primed for skiing. However, more snow also creates more challenging climbing conditions and higher avalanche danger.

　　Hazards in the Himalayas have been ratcheting up with climate change. Crevasses in the ice falls are getting wider and deeper, while warmer temperatures have made rock and ice fall more frequent. Historical routes have become more technical, including over the Khumbu Icefall, the most common way to the summit.

　　Traffic jams from commercial expeditions on the south side of Everest have likewise compounded the dangers there. The Nepali supreme court recently ordered a cap on permits for the mountain, for which the Nepali Department of Tourism is responsible for, but has yet to meaningfully enact. Skiers climbing Everest from the north side will still encounter a crowded summit from guided parties climbing the Khumbu route.

　　Conversely, the Tibetan, or north side of the mountain, is controlled by China, and nowadays is mired in restrictive bureaucracy that makes a modern-day attempt on the Hornbein Couloir even harder.

　　Climbers hopeful for permits for Everest’s north side have been navigating an opaque permitting process since China officially reopened it to foreign nationals in 2024 after the pandemic. Multiple parties from around the world have reported being denied permits, splintering some groups, and shutting down others outright.

　　The China Tibet Mountaineering Association issues both climbing and skiing permits, without a clear quota. However, the Chinese government states online that, “In 2019, a total of 362 people climbed the north slope of Qomolangma [Everest]: 142 foreign climbers, 12 Chinese ones, and 208 Nepalese Sherpa support personnel.”

　　In addition to climbing and skiing permits, plus a Chinese visa, authorities also require a Tibetan travel permit, and an alien’s travel permit for the Tibet Region. None of which are cheap. It costs tens-of-thousands of dollars just to look at the north side of Everest.

　　Then there are other new rules that make it even more complicated to try the Hornbein. There’s a one-to-one guide-to-client ratio required at altitudes above 23,000 feet, and supplemental oxygen is also now mandatory, which can be tough for skiing—the extra weight and face mask are cumbersome and claustrophobic.

　　Americans Hilaree Nelson and Jim Morrison did however ski the Lhotse Couloir with oxygen masks in 2018—a formidable 2,500-foot 50-degree hallway dropping from the summit of the fourth-highest mountain on earth—so its not impossible.

　　The Greatest Line Never Skied If you ask Perret, he’d tell you that rules are meant to be broken.

　　“It’s the most magnificent and challenging line,” he beams. “I hope whenever someone does it, they do it in alpine style. … You carry oxygen to basecamp to keep up appearances, and no one’s going to chase you up the mountain from there, you can just leave them behind.”

　　Of course, testing the forgiveness of the world’s most authoritarian super power by requiring porters and supplemental oxygen to ski in alpine style is a daunting extra layer to fold into an already perilous and costly expedition. But, the world’s most ambitious ski line is out there, dangling in the Death Zone, and that’s what it might take.