They weren't at 801mph airspeed. The article didn't make it clear exactly, but: "The Boeing 747-436 reached speeds of 825 mph (1,327 km/h) as it rode a jet str

They weren't at 801mph airspeed. The article didn't make it clear exactly, but: "The Boeing 747-436 reached speeds of 825 mph (1,327 km/h) as it rode a jet stream accelerated by Storm Ciara." Ie max ground speed 1327km/h. And: "The jet stream reached speeds of 260 mph (418 km/h) on Sunday morning, according to BBC Weather." So if their max ground speed coincides with max wind speed and the wind was perfectly tail, their air speed would have been closer to 909km/hour.