Aircraft–drone proximity: how Layer400 measures it
How Layer400 evaluates observed aircraft–drone separation, checks fresh reports, handles altitude uncertainty and distinguishes alerts from confirmed incidents.
By Layer400 · Reviewed
What the alert means
An observed aircraft–drone proximity alert means eligible received positions meet Layer400’s proximity rule. It is not a confirmed near miss, a prediction of collision, or evidence of a pilot’s intentions. The public feature evaluates the live tracks loaded in the browser, not every report held anywhere in the network.
The current observed-distance policy enters at 2,000 ft (609.6 m). The panel states whether it is using estimated three-dimensional separation or horizontal distance. These are different measurements and must not be reported interchangeably.
Freshness comes before distance
Both reports must be no more than ten seconds old and their observation times no more than three seconds apart. Invalid positions, stale or inconsistent reports, simulated data and known excessive position uncertainty are rejected. The calculation uses reported coordinates, not the marker’s animated display position.
One close sample is not enough. Both tracks must supply independent new observations, at least 750 milliseconds apart, within the confirmation window. Repeatedly receiving the same snapshot does not create extra evidence.
Horizontal and three-dimensional separation
Horizontal separation is the distance between the two reported positions across the Earth’s surface. Estimated three-dimensional separation also uses their vertical difference, but only when both heights have a sufficiently reliable common mean-sea-level reference.
The engine accepts qualified geometric or QNH-corrected sources with the required confidence and uncertainty metadata. Combined vertical uncertainty must be no more than 60 metres. It does not subtract a drone’s raw height above ground from an aircraft’s uncorrected pressure altitude. Without compatible heights, the panel explicitly uses horizontal separation.
For example, two markers could be close on the map but at very different heights. A horizontal alert alone does not establish that the vehicles passed within 2,000 ft in three dimensions.
When an alert ends
Fresh observations must remain above 2,250 ft (685.8 m) for five seconds before the event clears through separation. This wider exit threshold prevents rapid on/off changes around the entry boundary. Missing evidence ends availability; it does not prove the pair separated safely.
The graph shows up to two minutes of browser-session evidence. Gaps and changes in measurement method break the trace. The browser retains bounded state, with a maximum of 200 active events and a per-evaluation comparison budget. A limit warning means the evaluation is incomplete.
What you can and cannot conclude
The red highlights help you inspect a pair, its timestamps and the current distance method. TEST broadcasts stay labelled and are ranked after real traffic. Live overlays do not provide durable event records, background monitoring or a guaranteed network-wide alerting service. This observed rule is separate from any server-side predictive conflict calculation.
For retrospective work, use playback details and check the loaded time window and recording gaps. Do not relabel an alert as a confirmed incident without independent evidence. Read how reports reach the map.