Tall order

The Soviet withdrawal left China to figure out many problems on its own, Yuan said. Amid a period of severe economic difficulties, the government allocated $700,000-approved by then-Chinese president Liu Shaoqi and premier Zhou Enlai — to purchase mountaineering equipment from Europe.

Yet, without firsthand knowledge of Qomolangma's terrain, the purchasers relied on British expedition notes, guessing at equipment needs. This led to imprecise calculations for critical items like ropes and oxygen tanks, forcing last-minute purchases with compromised quality and suitability, Yuan added.

Despite all preparations, Qomolangma's north slope — dubbed "impassable even for birds" — was generally believed to be insurmountable, as it pushed every climber to their limits with its thin air, monthslong climbs, brutal winds, freezing cold and treacherous terrain.