Why doesn't PilotAware do ADS-B out?

November 9, 2020

At PilotAware we have been asked why we dont develop PilotAware to transmit ADSB-out at 1090MHz as this is the frequency used by the CAA for products compliant with, the UK only, publication CAP 1391.

The answer is that PilotAware has been consistent in its response that it will not make the considerable investment to produce such a UK only device until it has been shown that the 1090MHz Aviation Band, has the physical capacity to cater for all GA and CAT aircraft let alone drones transmitting on this frequency. PilotAware, like ICAO, the FAA in the United States and EASA in Europe, think that this is unlikely. Aviation transponders, that is, Mode-A, Mode-C, Mode-S and ADSB-out, all use the same 1090MHz band with its inherently limited capacity modulation technique, pulse position modulation (PPM).

In fact, in December 2019, the FAA in the USA have made it quite clear that they intend to prohibit the transmission of 1090MHz from drones for the same reasons.

The proposed rule also prohibits the use of ADS-B Out and transponders for UAS operations under 14 CFR part107 and part 91 unless otherwise authorized by the FAA. The FAA is concerned that the potential proliferation of ADS-B Out transmitters on UAS may negatively affect the safe operation of manned aircraft in the airspace of the United States. The projected numbers of UAS operations have the potential to saturate available ADS-B frequencies, affecting ADS-B capabilities for manned aircraft and potentially blinding ADS-B ground receivers.

For completeness, context and reference, read the full consultation paper from which this comes by following the link below.


In November 2020 the CAA produced CAP 722 Edition 8 which states in section

Under existing arrangements, ADS-B devices exchange information at 1090 MHz. However, this could lead to spectrum congestion in low level airspace. ICAO has issued a letter to States prohibiting the use of 1090 MHz below 500 feet. The UK is currently exploring the use of 978 MHz for UAS to mitigate the risk of spectrum overloading at 1090 MHz.

It is not just PilotAware who is being reluctant to invest. As recently as December 2019 a report was issued by AOPA. A digest of which is reproduced below.

‘AOPA-Netherlands has attempted to set up an experiment (similar to those in the UK and Denmark) to test ADSB equipment but the Dutch Ministry of Transportation wants to wait until EASA makes up their mind.

At this moment it is not at all clear what course EASA will take. An attempt has already been made years ago to implement ADS-B for all aircraft, also below 5700kg, but they had to realize that it can´t work based on Mode S [109MHz] technology for all.

In the European Core Area (within the polygon Paris → London → Hamburg → Vienna → Zurich → Paris) theMode S saturation is already so high, that equipping all remaining GA aircraft and air-sports-vehicles like sailplanes and microlights with Mode S based ADS-B would lead to overstressing the Mode S system. For instance in Germany on a nice summer-weekend when 25% of the GA fleet would become airborne at the same time, ATC would already have a massive problem. Targets could become invisible for a couple of seconds, and also the ACAS system on board of the airliners would only work with decreased range.

As a consequence EASA is considering other ADS-B enablers with higher capacity, one of them would be UAT, but they are also discussing about the integration of FLARM and other sources via their ground-system Open GliderNetwork.’ Ends.

For completeness and reference, the actual document can be found using the link below.


As supporters of PilotAware know, we also are champions of ground-based networks and have invested significant amounts of time money and energy in developing the PilotAware Grid Network to increase the necessary interoperability between existing systems, for the benefit of all. Read all about this and how you can help here.

If however, you have a modern Mode-S transponder such as a Trig or a Funke with extended squitter capability it makes eminent sense to connect an approved or unapproved GPS to it and thereby use its full functionality and enjoy the addition of ADSB-Out. We, therefore, encourage everyone who can, to do this and have included software in every PilotAware product or the last 3 years to make this both easy and inexpensive. How this can be done is explained here. Any form of situational awareness is good to help with your primary responsibility through the mandatory visual scan.

Blog Summary;

ICAO, FAA, EASA, CAA are all concerned that using 1090Mhz with its unchangeable, inefficient modulation technique as a standard for all Commercial, GA, Drones and other flying machines will lead to spectrum congestion and make it unworkable.

PilotAware agrees with this position and believes that 1090MHz should be reserved for commercial operations in controlled airspace for heavy aircraft as it is mandated today.

978MHz is the other aviation frequency that could possibly be used but this is not yet freely available for EC use in Europe.

PilotAware. See more aircraft than any other system.

-The PilotAware Team

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