Published by NATS today ( https://www.nats.aero/news/enabling-ads-b-out-for-general-aviation-gathers-pace/ ) :
Enabling ADS-B OUT for General Aviation gathers pace
Efforts to help private pilots enhance their situational awareness continue to progress following analysis of the CAA’s simultaneous surveillance trial and the release of new EASA standard modification procedures.
The trial took place last year to understand the consequences of transmitting Mode S and ADS-B data from different on-board devices at the same time. Analysis delivered promising but also unexpected results, which required further investigation and delayed publication of the report until now.
It was found that some Mode S extended squitter capable transponders actually transmit ADS-B data without the pilot’s knowledge under certain conditions. This can essentially corrupt the reported position accuracy, quality indicators, level data and Mode A code when received alongside the intentional ADS-B data from the separate on-board transmitter.
In all other respects, the original trial delivered very promising results, but it is important to ensure that aircraft do not transmit ADS-B from two devices at the same time. NATS, the CAA and Airspace4All have worked together to find mitigations for the problem and a new trial to prove their effectiveness is now underway. With these mitigations in place, simultaneous surveillance may offer some General Aviation pilots another way of helping themselves to be seen, and to see others.
The simultaneous surveillance trial report comes as EASA moves to encourage the transmission of ADS-B by introducing a standard modification to connect a GPS source to an ADS-B capable transponder. Three different GPS types are covered by the standard modification to suit a range of budgets.
NATS, the CAA and EUROCONTROL worked with EASA to draft standard modification CS‑SC005a, and a significant number of aircraft owners with ADS-B capable transponders can now take advantage of it, with the view that the more aircraft that are electronically conspicuous to other airspace users, the safer it is for everyone in the air.
Details of standard modification CS-SC005a can be found on the EASA website.