Below condensed excerpts from a May 2018 report covering 56 pages by the European Commission’s SESAR project. We will comment on the findings later as they may be surprisingly disappointing for many GA pilots regarding the purpose, effectiveness and maturity of the ADS-B framework, namely in the context of airliners.
In environments with dense traffic, such as Europe or the continental US, ADS-B has faced challenges. Thus, the term ‚the execution of an ADS-B recovery plan‘.
The original variant of 1090ES ADS-B was RTCA DO-260 (also known as version 0); early adopters equipped to that standard in the rushed ADS-B implementation. The original standard was inadequate, and the standard was updated twice to DO-260A (known as version 1) and DO-260B (known as version 2).
Since 2010, both US and the EU, have promulgated airborne mandates, which have gone through a series of revisions and postponements to finally converge on the currently applicable scopes (generally medium and heavy commercial traffic in the EU and including GA operating in controlled airspace in the US, several exceptions apply e.g. for state and military aircraft) and deadlines (2020 in both cases). In terms of these mandates, this is referred to as ADS-B Out. ADS-B In is not in the scope of the Regulation. European GA is out of the scope of EU mandate.
Airlines are affected by the misalignment of ADS-B mandates, especially between EU and US. European global airlines must equip their fleet to cope with the US mandate which requires to modify the Multi-Mode Receiver (MMR) by including the WAAS (Wide Area Augmentation System) function. In the US, additionally Selected Availability (SA) Aware MMR`s are required by 2020, and GPS Service Availability Prediction Tool and GPS augmentation WAAS/SBAS by 2025.
Airliner Equipment levels
Many aircraft are not fulfilling the quality requirements defined in the EU Regulation. The retro-fit plans show very few airlines planning to be compliant by 2020. The situation is similar for Regional and Business Aviation: there are no plans to retrofit their fleet, with very few exceptions.
Only around 20% of the EU airliners fleets are compliant with DO-260B, the majority of these are forward-fit on new deliveries. This is in line with the Airbus aircraft equipage rate (21% for A320, 31% for A330/A340). For the long-haul aircraft, 17% of the fleet is equipped, whilst for the short / medium haul aircraft, 21% is compliant with the Regulation. Data shows a consistent equipage level of 20% between mainline carriers and business aviation, with regional carriers falling behind that at 15%.
For the regional fleet, and especially Turboprops, ATR is offering the DO-260B compliance as an option on ATR’s-600 fleet, which is the last certified version. Regarding ATR-500 fleet, a retrofit solution should be certified by end of 2018.
For the long-haul fleet, some airlines are planning to retrofit their aircraft to comply with the Regulation. However, for the medium/short haul fleet, major airlines foresee difficulties to retrofit due to the high number of aircraft needed to be equipped in the short-term.
Technology and Capability
In the short to medium term, Mode S radars offer enhanced performance and substantial RF capacity improvements, whilst multilateration offers a cost-effective alternative to radar with similar performance to ADS-B.
ADS-B as a surveillance technology could not be able to fully replace conventional sensors until all airspace users are equipped and capable.
ADS-B was proven easily eavesdropped and/or spoofed when compared to conventional surveillance sensors. This raises substantial concerns to actors who value operational security or privacy. Technological mitigations are yet to become part of the global standard.
ATC Equipment levels
The current situation on ADS-B receiver installation in Europe is fragmented. Except for isolated areas such as oil rigs in Norway, no country today operates an ADS-B ground infrastructure for enroute surveillance integrated into the ATM system. France and other countries have no ADS-B ground coverage at all. France currently plans to install one single station in the Bordeaux area.
France, Luxembourg and several other countries do not have deployed ADS-B stations at their main airports today. Only a few countries today (mainly Germany and Switzerland) use ADS-B ground infrastructure for airport surveillance on few major airports, integrated into the ATM system.
UK, Belgium, Sweden, Finland and other countries will implement ADS-B ground reception without making operational use of the ADS-B data. In UK, France, Belgium, Italy, Sweden, Finland and other countries, stakeholders may intend to implement ADS-B for validation purposes or for surveillance of airport surface vehicles but there are no plans to integrate ADS-B position in ATC systems and to use it for ATC services.
Radio frequency spectrum is a scarce resource. Management of the spectrum is handled globally by the International Telecommunications Union (ITU) where States are represented. Aviation only has a status as an observer in ITU and is not part of decision making. Aviation is represented by States that often have other priorities to consider.
The aviation spectrum is attractive to telecommunication service providers. Traditionally, it was sufficient for aviation to claim ‚flight safety‘ to protect its spectrum, but during the last 20 years, a strong pressure has emerged from satellite service providers, mobile phone industry, broadcast companies etc., demanding access to aviation spectrum. The argument used against aviation is that the reserved spectrum is underutilized because of expected new systems not in operation and low spectrum efficiency due to old and obsolete technologies. The aeronautical band 960-1215 MHz is coming under increasing pressure to allow channel sharing with non-aviation services that by design are not compatible with the aeronautical applications incumbent in the band.
Radio channel saturation largely became a function of traffic density. Both TCAS and ADS-B use random channel access. The practical effect is that when the channel becomes saturated, the operational range of ADS-B in that location is substantially reduced.
Saturation of the 1090MHz channel is a regular occurrence in European airspace. The progressive rollout of the more spectrum efficient Mode S radars in lieu of old Mode A/C units alleviates this issue, but the freed capacity is being taken up by ADS-B with its rigid band usage character. TCAS is a significant contributor to channel congestion and can amount to 50% of radio traffic in a dense environment.
There exists a concrete risk of band oversaturation in the transitionary period when all aircraft are expected to both broadcast ADS-B and reply to Mode S interrogations on the same channel.
The position can be sourced from the aircraft’s inertial platform, i.e. does not need to come from GNSS. Such position quality will start to degrade after some time and the accuracy will be downgraded.
If surveillance is to make itself largely dependent upon GNSS by replacing ground-based surveillance sensors (radar, multilateration) with ADS-B, the shared dependency will lead to a significant common point of failure, since ATC is no longer able to determine aircraft positions. In the absence of an independent positioning source, both the aircraft crew and the ground ATC have effectively become blind. The consensus in the ATM community is that a robust, fully GNSS independent positioning and timing solution of some form will be necessary to provide some level of sustained operational capacity.
GNSS is a relatively fragile system; its weak received power makes it easy to interfere with, obstruct and spoof. Multiple cases of each have been demonstrated in the recent years and the number of interference events has been showing a sharply rising trend.
DO-260B ADS-B uses GNSS as its primary positioning source. The only two operational constellations in existence today being military systems each owned, operated and fully controlled by the US and Russia, and the relative vulnerability of GNSS to interference and spoofing raised unresolved questions of state liability and approval. US GPS and Russian GLONASS are provided realistically on an as-is basis with an expression of commitment from the respective federal administrations. This raises a dilemma concerning the role of national authorizations or approvals of these foreign-power controlled systems for use in the provision of safety of life services such as ATC.