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  • Andreas

OCAP and ADS-L


The main objective of the OCAP project is to provide GA pilots flying non-commercial aircraft with an easily available tool to help warn of possible collisions (see - be seen - and -avoid).


In principle, there are several ways to achieve this goal. The first possibility is that a holistic picture of the airspace is created on the ground and potential collisions are calculated and communicated to the aircraft, for the pilot to then take avoiding action based on information provided from the ground to the cockpit. A second option is for onboard equipment to calculate potential collisions themselves onboard the aircraft – again for the pilot to take avoiding action.


The OCAP project uses the second option. Aircraft transmit information about their flight path (broadcast) and receive information from aircraft in the vicinity (receive). They regularly calculate the aircraft’s own flight path and the flight paths of received aircraft, check whether possible collisions are imminent (predict) and warn the pilot. Two things are needed to do this:

  • A standardized format in which aircraft exchange data (position, direction and speed, acceleration or curve shape) with each other (broadcast / receive).

  • An algorithm to generate collision warnings for the pilot from the data received and the aircraft's own data (predict).


At European level, the EASA (European Union Aviation Safety Agency) published a first version of the open standard "ADS-L" in December 2022 (see ADS-L, ADS-L 4 SRD860 Issue 1). ADS-L aims to make manned, non-commercial aircraft visible, especially to U-Space Service Providers who’s role it is to manage the airspace used by drones.


ADS-L was not primarily developed for communication between aircraft or for collision warnings. However, there are various reasons why it makes sense to re-use the protocol for this purpose in the future, for example:

  • The radio packets defined in ADS-L already contain most of the information required for collision prediction, such as position, flight direction and speed of the flying object.

  • A uniform Europe-wide standard such as ADS-L enables a cross-border solution and thus simplification for pilots.

  • The radio spectrum is a limited resource. Sending different radio packets for different protocols increases the load on the spectrum and energy consumption at the transmitter. It is therefore more efficient to use and supplement ADS-L instead of developing a new, additional protocol.


The OCAP project will work with EASA to include information for collision prediction in the sense of see-and-avoid in a future version of ADS-L, without compromising the original purpose of ADS-L.


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