CAA/Ofcom statement on 978 MHz for drones

Ofcom and the UK Civil Aviation Authority (CAA) are making the 978 MHz spectrum available for airborne transmission onboard drones.

This move will enable the use of additional safety equipment, known as a Universal Access Transceiver or UAT. These safety devices make other aircraft aware of a drone’s position to enhance situational awareness.

This change supports longer distance operations, such as going beyond visual line of sight (BVLOS), and is part of a wider Government Future Of Flight action plan and the CAA’s Airspace Modernisation strategy.

Use of the 978 MHz frequencies for UAT is standardised internationally, and Ofcom’s licence includes a reference to the relevant CAA document (CAP 1391).

As such, the supplementary amendment within CAP 1391 - Electronic Conspicuity Devices - sets out specific conditions of use for drones utilising the 978 MHz UAT frequency. It states:

'The 978 MHz frequency is used only on-board Specific Category UAS operating BVLOS.

'The device should function in accordance with the RTCA minimum performance standards DO-282B. It is expected that DO-282C will be the standard from 2027.'

'A callsign for the Unmanned Aircraft (UA) should be allocated and agreed with the CAA, and an appropriate 24-bit aircraft address will be allocated where necessary on a case-by-case basis.'

The amendment adds that a detailed specification of the UAT equipment must be declared to the CAA RPAS sector team during application for a Specific Category authorisation, and the 978 MHz UAT frequency shall not be transmitted from a manned aircraft.

A 978 MHz frequency licence is available for £75 from Ofcom's website.

What Are UATs?

A Universal Access Transceiver (UAT) is a type of Automatic Dependent Surveillance–Broadcast (ADS-B) system that operates on 978 MHz.

In this context, a drone equipped with a UAT will broadcast its position and identity.

How will a UAT benefit BVLOS drone operations?

The use of UAT on 978 MHz brings significant advantages for BVLOS drone operations, particularly in improving safety, scalability, and regulatory compliance.

UAT allows drones to be 'seen' by other aircraft and provides the necessary tracking and communication capabilities over long distances., reducing the risk of mid-air collisions.

This is essential for BVLOS operations where the drone pilot cannot rely on direct visual observation.

As such, UAT on drones ensures compliance with evolving regulations for safe and scalable BVLOS operations.

What is CAP 1391?

CAP 1391 is a regulation set by the UK CAA that establishes the standards for electronic conspicuity (EC) devices used in aviation.

These devices help aircraft, drones, and other airspace users detect and communicate their position to improve airspace safety and reduce the risk of collisions.

The goal is to enhance situational awareness for pilots and air traffic control.

What are DO-282 standards?

The DO-282 series, published by the RTCA (Radio Technical Commission for Aeronautics), defines the Minimum Operational Performance Standards (MOPS) for UATs used in ADS-B systems.

These standards are crucial for ensuring the safe and efficient use of 978 MHz ADS-B technology, particularly in general aviation and drone operations.

The most recent version is DO-282C, which updates and refines previous versions (DO-282, DO-282A, and DO-282B).

These standards:

• Specify performance requirements for UAT ADS-B systems, which operate on 978 MHz.

• Ensure that ADS-B transmitters and receivers meet reliability, accuracy, and interoperability standards.

• Are an updated version of previous RTCA standards, improving system performance and compatibility.

Changes to rules on PMSE sharing

The frequencies used at 978 MHz are part of an aeronautical navigation band that is currently shared with low-power radio microphones used for programme making and special events (PMSE).

The sharing arrangements were introduced in Ofcom’s 2016 Statement on New Spectrum for Audio PMSE. That Statement made it clear that, as the aeronautical use changes, the availability of PMSE spectrum will be updated, in a way that maintains aeronautical safety, via agreement with the CAA.

Following established processes, Ofcom and the CAA have agreed to update the availability of the PMSE spectrum. The following changes have taken effect:

• PMSE for outdoor events between the frequencies of 976.5 to 979.5 MHz will no longer be licensed.

• Frequencies for indoor PMSE use will continue to be licensed, as the likelihood of interference into UAT in this situation is negligible and the likelihood of interference into indoor PMSE is extremely low.

• Additional PMSE use is allowed at the following additional frequencies: 1015-1016 MHz; 1044-1045 MHz; 1075-1076 MHz and 1104 to 1105 MHz.

The addendum to the Spectrum Management Rules for this band can be viewed here.