A helicopter hovering or circling overhead is one of the most-asked "what is that?" questions, and usually has an ordinary answer. Many helicopters broadcast ADS-B just like aeroplanes, so AeroScope can often tell you what it is and what it’s doing. Here’s how, and the honest exceptions.
Circling a wide area, often at night, supporting an incident on the ground. Some forces limit what they broadcast.
Orbiting a traffic incident, event or breaking story to get a stable camera shot.
Transiting fast and low, or landing at a scene or hospital. Time-critical, so direct routing.
Transit or training. Flagged from ICAO hex and callsign, see military over my house.
Slow, methodical grid or line-following for power lines, pipelines, mapping or aerial photography.
Point-to-point transport or sightseeing, often broadcasting full identity.
| Operator | What you will notice |
|---|---|
| Air ambulance / HEMS | Arrives fast, lands somewhere unusual such as a field or road, then departs. Often the loudest and lowest helicopter you will hear. |
| Police | Orbits an area at moderate altitude, sometimes for a long period, frequently at night. |
| News and media | Orbits a traffic incident or event, usually in daylight and usually briefly. |
| Powerline and pipeline patrol | Flies slowly along a linear route rather than circling. |
| Training | Repetitive circuits and hover practice near a heliport or airfield. |
| Offshore and utility transport | Straight point-to-point transits, common near coastlines. |
Helicopter visibility on ADS-B is genuinely patchier than fixed-wing aviation, and it is worth knowing why before concluding something is being hidden.
So a helicopter you can clearly hear may legitimately not appear. That is a limitation of ADS-B, not evidence of anything. See limitations.