The September 2022 update to the EASA document Easy Access Rules for Unmanned Aerial Systems, describes all aspects of UAV operations for VLOS and BVLOS operations. The overriding message is that ‘operations should be as safe, if not safer than manned aviation’. However, the burden of proof to ensure safe flights remains with the Operator.
To achieve this, all aspects of the quality and competence of UAS activities are required to be demonstrated.
The EASA document takes a pragmatic approach in confirming that ‘the rules and procedures applicable to UAS operations should be proportional to the nature and the risk of the operation …. and to the operational characteristics of the UAV concerned and the characteristics of the area of operations.’
Prospective European operators are aware that, three categories of operations, increasing in level of risk, are defined. These are ‘open’, ’specific’, and ‘certified’.
In brief, the ‘open category’ covers operations that present the lowest risks and should be conducted using the UAS classes that are defined in Commission Delegated Regulation EU2019/945.
Operations in the ‘specific category’ should cover other categories that present a higher risk and for which a Specific Operations Risk Assessment, (SORA) should be conducted to indicate which safety requirements are necessary to keep operations safe.
Operations in the ‘certified category’ should as a principle be subject to rules on the certification of the operator, and the licensing of remote pilots, in addition to the certification of the aircraft pursuant to Delegated Regulation (EU) 2019/945
Whilst the categories differ they all operate in a defined Operational Volume that is made up of the Flight Geography Volume, the Contingency Volume and the Ground Risk Buffer Area to provide operational and safety zones.
Each individual Operational Volume has an Air Risk Category. This includes the probability of a collision with other aircraft in the class of airspace used.
There are four ARC categories.
ARC-a is generally defined as airspace where the risk of a collision between a UAS and a manned aircraft is acceptable without the addition of any mitigations to improve safety.
ARC-b, ARC-c, and ARC-d define volumes of airspace with an increased risk of a collision between a UAS and a manned aircraft. These areas require either Strategic or Tactical Mitigation to improve inherent safety levels.
The Air Risk Category (ARC-n) is usually established by the Competent Authority. However, if one has not been established then this is done by the use of a Specific Operations Risk Assessment SORA completed by the Operator.
The Initial ARC is a generalised qualitative classification of the rate at which a UAS would encounter a manned aircraft in the specific operational volume.
However, it is recognised that the UAS operational volume may have a different collision risk (possibly lower) from the one that the generalised Initial ARC was assigned. Consequently, this Initial ARC may be reduced through risk mitigation actions.
These need to be demonstrated positively through evidence, by the Operator or the Competent Authority. If approved, reducing the Initial ARC through risk mitigation has significant benefits to the Operator. The Residual ARC is the classification after all Strategic and Tactical mitigations are agreed upon and applied.
The types of mitigation are classified as;
I. Strategic Mitigations, implemented by the application of operational restrictions
II. Strategic Mitigations, implemented by the application of common structures and rules
III. Tactical Mitigations.
Strategic mitigations are applied before the UAV takes off and are either;
a) under the control of the Operator (mitigated by operational restriction).
b) not under the control of the Operator (mitigated by common rules and structures).
Tactical mitigations are applied after take-off and are used to reduce the risk of a collision during flight. The following diagram shows the relationship between Strategic and Tactical Mitigations.
Strategic Mitigations, supported by Common Flight Rules and Common Airspace Structures, are extremely important to reduce air conflicts or make conflict resolution easier. However, it is the more dynamic Tactical Mitigation provided by the situational awareness available from the PilotAware Infrastructure that can reduce the risk of in-flight collisions. This is the subject of this document.
In an ideal world, a common, modern, universal electronic conspicuity standard, working on a single frequency would be used by all aircraft to allow full interoperability. Unfortunately, due to historic, operational, physical and financial constraints, this is not possible. Consequently, all types of electronic conspicuity devices in use today must be detected for complete situational awareness. These different types include; Mode-S, ADSB(DF17), UK Only CAP1391(DF18), PilotAware, FLARM, OGN trackers, Fanet+ and mobile device applications.
The following diagram, taken from Easy Access Rules for UAS, shows that ARC-a does not necessarily need mitigation. Also as ARC-d is in controlled airspace, the operator will be under the direct control of the responsible ATC similar, to that provided to a manned aircraft. For both the ARC-b and ARC-c and to some extent ARC-d classifications, PilotAware infrastructure can provide help for both Strategic and Tactical Mitigation.
Tactical Mitigation of air risk includes the implementation of the ‘Detect and Avoid’ principles derived from traditional ‘See and Avoid’ techniques enhanced with Electronic Conspicuity.
The phases of Detect and Avoid are; Detect – Decide – Command – Execute – Feedback.
In a fully autonomous system, all of the above phases are automatic and independent of the type of Electronic Conspicuity used by other air users in the Operational Area. Whilst this is a future aspiration, PilotAware technology is available now to enable Operators to meet the required TMPR and reduce the ARC accordingly through direct Operator involvement.
The following diagram shows the TMPR requirement for all ARC classifications. To meet these requirements, within the Operational Volume, one must be able to detect 50% of all aircraft in ARC-b and 90% of all aircraft in ARC-c. The detection of all classes of aircraft and Electronic Conspicuity is required to do this safely.
The challenges to doing this are to accurately and cost-effectively;
I. Detect all classes of aircraft transmitting any of the EC genres, voluntarily chosen by European pilots.
II. Overcome topographical signal obscuration due to hills, high buildings, moisture and temperature.
III. Overcome airframe signal obscuration blocking the UHF signals transmitted by all Electronic Conspicuity devices.
IV. Provide technology with sufficient nodal redundancy to overcome single-point failures in detection.
V. Detect other UAVs using any EC down to ground level.
VI. Reduce latency and refresh rates to a minimum across all data paths
VII. Provide real-time and near real-time information preferably in both directions through interoperability.
In the UK and Europe, PilotAware infrastructure uses multiple Access Nodes to collect data from low-flying aircraft transmitting one, or more, of the major cooperative Electronic Conspicuity signals linked to a common ICAO address. These are ADSB (DF17) from a transponder, ADSB (DF18) from a CAP1391 transceiver (UK only), Mode-S, Fanet+, OGN trackers, FLARM, PilotAware and mobile applications. The diagram below shows one element of the PilotAware infrastructure – the ATOM ground station.
PilotAware has been developing Electronic Conspicuity and Situational Awareness systems since 2016. During this time it has become apparent that simple single point-to-point solutions do not provide sufficient integrity and redundancy to be able to consistently and continuously track all classes of aircraft and EC types. Particularly at low levels. This is due to the nature of the UHF signals transmitted which are affected by attenuation and blocking due to airframe and topographical obscuration.
PilotAware has developed and refined technology using multiple paths from multiple technologies to overcome this. The overall technology detects aircraft transmissions using airborne and ground-based assets that; detect, re-broadcast and relay information to other users and to the PilotAware servers.
The positions of aircraft detected locally can be accessed from an individual ground-based Access Node or the data can be concatenated to provide a combined regional, national or continental view available from the PilotAware central servers.
Starting in the air, all PilotAware Rosetta EC devices will directly detect the location of other PilotAware users, ADSB and CAP1391 devices (where legal) and Mode-C/S transmissions as a bearingless target. This is done instantly with a line of sight range of 30-50 km. The single-board computer built into PilotAware in-flight devices records all aircraft detected on all flights on a continuous basis for onward transmission or archive when required.
To enhance this basic air-to-air detection, a network of ground stations with over 280 sites has been installed in the UK and a further 60 sites in mainland Europe. All PilotAware-equipped aircraft connect to one or more of these ATOM ground stations to mutually enhance their situational awareness of the local area.
The ATOM stations detect all aircraft transmitting FLARM, FANET+, ADSB, CAP1391, PilotAware and Mode-S signals (using multilateration) and rebroadcast their locations to the airborne PilotAware-equipped aircraft if required. All data collected at the individual ATOM ground station is also transmitted to the PilotAware servers using a low-latency encrypted software-defined GRID network.
In the UK, in addition to the 280+ ATOM ground stations, a further 1,300 ground stations from 360 RADAR Ltd are used to provide data on the position of low-flying Mode-S equipped aircraft using multilateration.
All ATOM ground stations are interconnected through the PilotAware software-defined GRID to provide greater integrity, redundancy and multi-path detection. Individual aircraft signals received by multiple ground stations and airborne assets are used to compensate for the airframe obscuration that affects simple point-to-point solutions and continually keeps the target aircraft in view for ATC situational awareness applications.
As discussed earlier, EC radio signals from low-flying aircraft and UAVs are susceptible to obscuration (blocking or attenuation) from topographical obstacles such as hills forests and urban high-rise buildings. To overcome this Sky GRIDTM technology, installed in PilotAware-equipped aircraft, detects and relays the location of low-flying PilotAware-equipped aircraft and UAVs. These relays are sent to ground stations and other aircraft to ensure that the data containing the location of the low-flying aircraft is available to other users and also sent to the PilotAware servers. In this way, the location of the low-flying aircraft or UAV is not lost to a user of the PilotAware infrastructure whether acting as a pilot in the air or a UAV operator on the ground.
In addition, information on the locations of all aircraft within a required operational area is relayed to the low-flying aircraft or UAV. Having this enhanced situational awareness view is especially useful in mountainous regions and for low-flying operations. This data, provided to a PilotAware-equipped UAV has been successfully used to drive Artificial Intelligence software to demonstrate the autonomous sense and avoidance of local aircraft independent of what EC they transmit.
PilotAware iGRID technology links airborne PilotAware devices to the PilotAware servers via the mobile network to ensure greater redundancy and reach, and record the position of all aircraft detected by every device.
All transmissions are time-stamped so that only the latest data is used ensuring the lowest latency. Data can be transferred from the PilotAware servers directly to the individual or multiple aircraft or UAVs, to ATC or to the UAV operator to show all detected aircraft in a required operational volume.
The diagram below shows the combined detection and reporting paths of the PilotAware infrastructure. This interlocking mesh infrastructure is highly intelligent and ensures high integrity and redundancy through multi-node and multi-technology integration. This ensures that single points of failure in the network are reduced wherever possible. All flight data is retained on the servers for onwards transmission ananalysis.
Using the PilotAware infrastructure described above, GA pilots using PilotAware devices receive quality information on more aircraft types than any other system. As shown the combined data from the ATOM GRID, Sky GRIDTM and iGRID ensure that the greatest possible continuous detection of aircraft, transmitting any form of EC, is achieved.
Transmissions from aircraft detected directly will be received at the speed of light with very little latency. Similarly, the rebroadcast of FLARM and Fanet+ data is detected at the speed of light with a few 10mS of delay being typical.
Mode-S-equipped aircraft are detected using the multilateration of their response to an SSR or TCAS interrogation, which can come from multiple sources. The refresh rate of the actual position shown is primarily caused by the 1030MHz interrogation rate. When the interrogation is from a single interrogator, this refresh rate is between 4-9 seconds. Sub-second latency is incurred for the multilateration calculation process. This is commensurate with the latency and refresh rates inherent in traditional Primary and SSR detection of Mode-S targets.
Latency within the Mobile network is more variable and depends on many factors including the region of operation, the aircraft's height, traffic density and range.
The PilotAware encrypted software defined GRID induces a low latency, with a few 100mS of delay being typical.
Using the multiple technologies described above provides a high level of availability and redundancy. The fidelity of the system will depend on the number and quality of the data-collecting assets available within the Operational Volume. The PilotAware technology that does this is available now for installation in your area.
We believe that we have demonstrated that PilotAware technology detects and presents the broadest amount of data from the widest possible range of aircraft. But how can this be best used, now and in the future?
There are many operational use cases and no one solution fits all. That which is suitable for continuous line monitoring will differ from UAV operations that need more flexibility in operation. However, a full situational awareness of all aircraft in the Operational Volume is required for tactical safety mitigation.
Whilst fully autonomous flight, controlled by AI is the ultimate goal, we have the technology today to provide the necessary data to provide situational awareness in the Operational Volume and beyond.
The Direct Detection, ATOM GRID and SkyGRID technology described above is available now for UAVs that are using an installed PilotAware Rosetta.
Rosetta weighs 230 grams and is powered by an external 5.2v 2.5V power supply. iGRID technology is also available if there is an accessible mobile connection on the UAV.
When using Rosetta a UAV Operator with internet access will have enhanced situational awareness of the Operational Volume as if he/she was sitting in the UAV that is under their control. In other words, local aircraft would appear referenced to the UAV in the centre.
In turn, the UAV would have the advantage of being shown on the remote USP screen as a unique UAV detected directly by the ATOM Ground Network or relayed through Sky GRID.
In normal operations, the UAV would be flying much lower than the manned aircraft. However, in the screenshot below the UAV is shown flying at the allocated 125M maximum height and taking advantage of the onboard Direct, ATOM GRID and Sky GRID technologies to have a full situational awareness of the other technologies.
The RADAR screen below is one of many visualisations that can be used. This one shows the UAV in the centre and the various aircraft in the operational volume. Vertical and Horizontal scales can be zoomed in or out as required. Real-time data can be readily imported directly into your application to enhance existing 3rd party maps of fixed objects and topology or moving maps.
Data is archived for post-mission analysis showing all detected aircraft that came close and how the UAV and the other aircraft responded.
Heatmaps of Operational Areas, and beyond can be readily produced to also provide evidence for Strategic Mitigation or to help reduce an area to a lower ARC than originally defined. This can be done in 4 dimensions across all EC and at predetermined low levels. For example here is a past 3 months' view of all aircraft detected below 500ft altitude in the Solent region of the UK.
The GA airfields at Sandown, Bembridge and Lee on Solent and areas of lower density can be clearly seen.
GA aircraft don’t generally file flight plans in uncontrolled airspace however, having anecdotal data of where the majority of flights coalesce in time and space will assist your route planning. Alternatively, areas of low flight density can be easily seen as evidence for ARC(n) Strategic Mitigation.
Hardware
PilotAware technology is extremely innovative and uses all technology genres to meet the aim of providing the best Operational Situational awareness possible. We have developed and are testing a smaller integrated version of Rosetta (DX) that weighs only 90 grams that has all the functionality of the GA Rosetta described earlier, thus contributing to the PilotAware infrastructure. Rosetta DX will be commercially available in 2023.
Within the Rosetta (DX) roadmap is the inclusion of a Mobile Tx/RX module to allow iGrid functionality for full two-way situational awareness for those UAVs that are not so equipped. All PilotAware technology is backwards compatible.
Software
During 2022 PilotAware and other manufacturers supported EASA in the development of the standard
SERA.6005 Requirements for communications, SSR transponder and electronic conspicuity in U-space airspace
the Whereby, Manned aircraft operating in airspace designated by the competent authority as a U-space airspace, and not provided with an air traffic control service by the ANSP, shall continuously make themselves electronically conspicuous to the U-space service providers.
Its objective is for manned aircraft to provide continuous position information to USSPs so that UAS operators can use it to eliminate collision hazards between manned aircraft and UAS operating jointly within U-space airspace.
EASA has subsequently through NPA 2021-14 published the draft Acceptable Means of Compliance (AMC) and Guidance Material (GM) to U-space regulations. One of the proposed technical means to comply with the new SERA requirement is transmissions of aircraft position from devices/systems using the SRD-860 frequency band. The draft specification AMC1 SERA.6005(c) describes further technical details of these transmissions to allow U-space Service Providers (USSPs) to receive transmitted information and process it in accordance with U-space regulations.
An additional objective of the draft technical specification is to improve the air-to-air interoperability of existing traffic awareness systems transmitting on the SRD-860 frequency band. PilotAware transmits on the SRD-860 band (869.525)
PiloytAware fully supports this approach by EASA and will be working to help them with full compliance.
Autonomous Flight
In September 2021 PilotAware and the University of Central Lancashire (UCLan) demonstrated autonomous UAV flight including the sense and avoidance of drones flying autonomously using the locations of nearby traffic supplied by the PilotAware Network. In this demonstration, it was shown that it is not necessary for the UAV to have the reception of all genres of EC if their position is available centrally with demonstrable low latency. Since this demonstration, PilotAware has increased the amount and integrity of traffic detected through the multiple nodes available with the introduction of Sky GRID and iGRID in 2022.
PilotAware and UCLAN are seeking partnerships to develop this concept further to bring this autonomous technology to market.
For more complete definitions, please view the EASA Easy Access Rules For Unmanned Aircraft Systems.
For more information on how PilotAware technology, on the ground, in the air and on the UAV can help you with your Operations now and in the future please email atom@pilotaware.com.
We will be pleased to help you open up your opportunities and maximise your innovation.