High-altitude balloons: slow drifts far above airliner traffic

Research and commercial balloons can climb above 60,000 ft and stay aloft for hours or days. Many carry ADS-B transmitters, so they appear in flight-tracking data with an altitude far above the airliners and a ground speed closer to a car's than a jet's. Their tracks wander with the wind instead of following airways.

The site looks for an aircraft that stays at 50,000 ft or higher for at least ten minutes, with a median ground speed of 80 knots or less and an altitude that changes slowly. It then wants corroboration: a geometric altitude that agrees with the pressure altitude, a lighter-than-air emitter category, a balloon type code, a callsign with a balloon prefix or a flight that lasts half an hour or more.

Balloon data has its own glitches. One report can show a ground speed above 1,000 knots between neighbors near 20, and the story labels such a spike as a data error. The data does not say who launched a balloon, what it carried or where it came down. Unmanned free balloons fly under their own FAA rules, described in the regulation listed below.