CAP 1391 specifies Electronic Conspicuity (EC) devices that have the ability to signal their presence to other airspace users, thereby turning the “see-and-avoid” concept into “see-BE SEEN-and-avoid”. It provides a technical specification for their production, as well as detailing the procedure for self-declaration that allows the device to be covered under a single UK national equipment approval. GA aircraft owners who have no requirement to equip their aircraft with a transponder may voluntarily use an EC device.
To meet the criteria for low cost and low power, EC devices use limited capability, low complexity, off-the-shelf components that do not meet classical aviation equipment requirements. Although this is reasonable for a device carried voluntarily as an aid to “see-and-avoid”, it also means that their transmitted data cannot be relied upon and, consequently, their design requires that any functional failures will result in a ‘No Safety Effect’.
However, GNSS receivers are now available that meet the intent of FAA TSO-C199 Class B for Traffic Awareness Beacon Systems (TABS), which are qualified to a recognised aviation standard and provide enhanced performance for relatively low cost. These robust receiver designs are capable of providing potential performance enhancements for EC devices, allowing them to report improved functional capability within allowable limits.
The CAA has reviewed the TSO-C199 Class B specification and test requirements, and amended CAP to formally recognise GNSS receivers qualified to this TSO as position sources that may be incorporated as part of EC devices or for connection to EC device transmitters.
A more comprehensive amendment to this document is expected late 2021.
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