What accuracy is required in todays ADS-B position reporting?

Question

I would like to know what accuracy is required for ADS-B position reporting.

For example, mobile phones A-GPS capable have 10 meter position error with perfect conditions.

Is this similar with ADS-B GPS receivers?

Answer 1

You can report any accuracy you want over ADS-B, as long as the position source is compliant with TSO-C129 (or later revision), TSO-C145a/C146a (or later revision), or TSO-C196 (or later revision).

ADS-B gives amongst others:

• a position,
• an associated Navigation Integrity Category (NIC) based on the GPS Horizontal Protection Limit; and
• an associated Navigation Accuracy Category for position (NAC_p) based on the Estimated Position Uncertainty / Horizontal Figure of Merit.

If the positioning system cannot provide integrity or accuracy, the ADS-B transmitter will encode the NIC/NAC as 0 (unknown). This warns users of the ADS-B data that the position source is not to be trusted.

In day-to-day operation, ADS-B is required to provide:

• an integrity limit less than 0.2 nautical miles;
• a reported accuracy of less than 0.05 nautical miles;

Practically, GPS will occasionally give lower accuracies / integrity, but it will be reflected in the NAC_p / NIC so that users of the data can decide how to handle this lower quality data for their purposes.

Mobile phone A-GPS chips are typically not certified under the TSO's mentioned above and they don't provide integrity information. These chips are thus not suitable for ADS-B.