Simultaneous transmission from Mode S transponders and CAP1391-approved ADS-B transceivers from the same aircraft is not currently permitted by the CAA.

However, the CAA has agreed an exemption, subject to conditions, for the Airspace4All GA Airfield ATS ADS-B Traffic Display Trial.

Obviously, where an aircraft already has an ADS-B Out capable Mode S ES transponder and the aircraft is already emitting ADS-B there is no requirement to also transmit ADS-B from a second device. The current CAA restriction therefore affects aircraft with Mode S transponders that are not setup to emit ADS-B Out.

As part of the Airspace4All Trial we are loaning out a number of CAP1391-Approved ADS-B transceivers (uAvionix SkyEchos) to selected operators at the trial airfields. These operators are being selected on the basis of maximising the airborne time of the transceivers. These operators will be invited to participate by the airfield or Airspace4All.

Where these operators have a non-ADS-B Mode S transponder in their aircraft, there is a further step before we can agree to loaning them an ADS-B transceiver.

The CAA are running a ‘Simultaneous Transmission Trial’ (STT) for Mode S/CAP1391 transceivers and these operators need to be accepted by the CAA onto this STT.

The process for seeking approval for the STT is as follows:
– The Mode S operator signs a Declaration for the STT (provided by the airfield).
– The Mode S operator submits details of their aircraft, including installed & portable avionics, to CAA (via an online form)
– CAA review the submitted details and grant or deny approval for the STT
– if approved for the STT the invited operator will be loaned the CAP1391-approved SkyEcho

CAA STT-approved operators must comply with the conditions of the STT Declaration at all times. Where the operator is a Flying School or Flying Club they must ensure that all their pilots fully understand the conditions of the STT Declaration and also comply fully.

Full details will be provided to all invited operators.