Can Every Aircraft Really Be Tracked by Satellite?

Aircraft broadcast their GPS position on 1090 MHz roughly twice a second. Historically this needed a ground receiver within a few hundred kilometres, which meant coverage stopped at the coastline.

Receivers were then placed on a constellation of low-earth-orbit satellites, listening for the same broadcasts from above. No change to the aircraft was needed — the equipment already fitted for ground ADS-B works unmodified.

The result is position updates over the Southern Ocean, the mid-Pacific and the poles at a rate comparable to radar coverage over a European city.

The visible benefit is not safety headlines but efficiency. Oceanic separation standards were built around the reality that a controller knew an aircraft's position from a voice report every 30 to 60 minutes. That uncertainty required large separation minima — aircraft spaced far apart in time and altitude.

With continuous surveillance, those minima have been reduced. More aircraft can fly optimal tracks at optimal altitudes rather than being held on suboptimal ones for spacing. The fuel and emissions saving across the North Atlantic alone is substantial.

The search-and-rescue benefit is real too: an aircraft in difficulty over an ocean now has a known position measured in kilometres rather than in hours of flight time.

ADS-B is dependent surveillance. The aircraft calculates its own position and chooses to broadcast it. Everything above works because the transponder is transmitting.

Switch it off and satellite ADS-B sees nothing, exactly as ground ADS-B sees nothing. The technology that closed the oceanic coverage gap does not close the cooperation gap.

This is why the post-MH370 requirements include autonomous distress tracking — a function that transmits position when the aircraft's state becomes abnormal, designed to be independent of the transponder and of crew action. It is the part of the response that addresses an aircraft that stops cooperating, and it is a much harder engineering and regulatory problem than adding satellite receivers.

Aircraft without ADS-B equipment — older general aviation, some state and military aircraft — are not visible this way. Military aircraft frequently transmit in modes that are filtered from public feeds, and some do not transmit at all.

And satellite ADS-B tells you where an aircraft says it is. If its navigation system is producing a wrong position, the surveillance reports the wrong position with high confidence. That failure mode is rare, and it is why independent surveillance — primary radar — retains a role in the busiest and most sensitive airspace.