Although the plane didn't remain in the "jet streak" - the zone of maximum wind embedded within the jet stream - for long, it still arrived 48 minutes early. And you might notice something suspect about the 801 mph reading - it's above the speed of sound. Commercial aircraft ordinarily can't break the sound barrier, because they're not designed to handle the sudden increase in drag and other aerodynamic effects associated with those speeds. Despite a ground speed that high, the plane didn't come close to reaching that threshold because it was embedded in the swiftly moving air.