Using NACp as a GPS/GNSS interference indicator
Low NACp is one of the clearest public aviation data signals for degraded GNSS accuracy. The key is to analyze regional patterns and avoid attribution claims.
NACp can be used as a GPS/GNSS interference indicator when many aircraft in a region report degraded navigation accuracy. It should be analyzed as an aggregate regional signal and not treated as proof of jamming source or intent.
Aircraft report navigation accuracy as part of ADS-B. When many aircraft in the same region report degraded accuracy during the same time window, the aggregate pattern can be a strong indicator of GPS/GNSS interference.
The useful signal is not one low-NACp aircraft. The useful signal is a regional share of degraded reports over a defined time window, checked against receiver coverage and aircraft mix.
A responsible method
- Define the region and time window before measuring.
- Count degraded reports consistently, using the same NACp threshold.
- Compare 1 hour, 6 hour, 24 hour, and 7 day windows to separate spikes from persistent patterns.
- Label results as interference indicators unless attribution is independently confirmed.