In 2014, Airbus needed to prove its boldest jet yet—the carbon-fiber A350 XWB—could shrug off the planet’s harshest climates. Instead of a lab, the company chose two very real frontiers: Bolivia’s sky-high runways and Canada’s Arctic chill. Over three hectic weeks, the second test aircraft, MSN3, would leap from thin-air takeoffs at 13,300 ft in La Paz to –28 °C predawn engine starts in Iqaluit, Nunavut, gathering the data regulators demanded and stories aviation buffs still trade on forums.