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Unmanned Aerial Vehicles

Unmanned aerial vehicles (UAVs), controlled from the ground, have the potential to deliver the biggest innovation for civil and military aircraft since jet propulsion. Lambert Dopping-Hepenstal FREng, programme director of the UAV project ASTRAEA, outlines how this far-reaching UK programme is addressing the technical, regulatory and societal challenges to the introduction of unmanned aircraft.

The disappearance of Flight MH370 over the southern Indian Ocean has sharpened the focus on the limitations of maritime reconnaissance aircraft in the search for wreckage. An area the size of Western Europe, none of it closer to land than 1,000 km, challenged the capabilities of the aircraft and the crews deployed to conduct the search. With limited range and inclement weather, aircraft spent more time travelling to and from the search area than on the search itself.

There has already been a great increase in the numbers of small unmanned aircraft being used for a wide variety of tasks, but within the next five to ten years, we may see much larger ones carrying out long-endurance flights in demanding conditions, such as search and rescue far out in the oceans. These vehicles could stay in a search area for the duration of the task, refuelled by other unmanned aircraft in order to pinpoint the target area.

The Thales Watchkeeper WK450 is a remote-piloted aircraft used by the UK Army for surveillance, reconnaissance and intelligence. In the latter stages of 2013, it became the first unmanned system to be certified by the military airworthiness authority for flying in appropriate airspace. The flights were overseen by military air traffic controllers © Thales

Unmanned aircraft need not be constrained by size, endurance and the operating limitations imposed by the need to protect a human on-board; they could fly for very long periods, in high-risk environments and could be of any shape or size. Small UAVs are already being used for surveying civil engineering projects, small-scale agricultural monitoring, filming at sporting events and police surveillance.

The potential uses for larger ones range from environmental monitoring to pipeline inspection, disaster relief and freight. The technologies that will spark this revolution will also help improve the safety, security and efficiency of manned aviation.

For all these benefits, it is neither reasonable nor economical to partition existing airspace to accommodate unmanned aerial vehicles (UAVs). Instead, we have to find ways to introduce UAVs alongside piloted aircraft so that they fly under the same rules and regulations. All the basic technologies to make this possible exist. The main challenge is the application and integration of these technologies to allow vehicles to be certified to share airspace with other piloted craft.


Unmanned aircraft are variously referred to as drones, remotely piloted aircraft systems (RPAS), unmanned aerial vehicles (UAVs) and unmanned aircraft systems (UAS).

Whichever name is preferred, the critical elements required are:

  • an airborne vehicle
  • a remote pilot station
  • a communication infrastructure
  • a launch and recovery system
  • In Europe, regulators divide unmanned aircraft into three types: small (below 20kg), light (up to 150kg) and large (more than 150kg). Technologies being developed in the ASTRAEA programme will potentially benefit all three types.


    Unmanned aircraft date back to the First World War, when radio-controlled aircraft provided aerial target practice. This continued to be their main use until a decade or so ago, when UAVs entered use for military reconnaissance and operations.

    These military unmanned aircraft, commonly called drones, were designed for military operations in segregated airspace. They do not, however, have on-board systems that would allow them to fly in general airspace. Before UAVs can be used for non-military applications, technologies and stringent regulations to ensure their safe flight in general airspace have to be developed.

    In the UK, commercial unmanned operations are currently limited to very small aircraft, generally weighing no more than 5kg, flown within direct line-of-sight of a ground ‘pilot’. These UAVs have to operate below 400 feet (120m) altitude and no closer than 50m to people and structures. While these limitations are manageable for small operations in agriculture, surveying, or for inspection of hazardous areas, they are too restrictive for many potential applications.

    Solving issues of airworthiness, operating procedures, situational awareness and communications infrastructure could pave the way for companies such as Amazon and DHL to realise their ambition to make ‘deliveries by drone’, and for Google to connect the developing world to the internet using high-altitude solar-powered drones.


    Airspace, by international agreement, is divided into seven classes, A to G, from high-level controlled air lanes to uncontrolled general airspace, where any air user can fly under Visual Flight Rules (VFR) and be responsible for their own safe separation from other users. Class G airspace, where the pilot is wholly responsible for collision and weather avoidance without the aid of air traffic controllers, will be the most challenging for unmanned aircraft.


    Over the past eight years, the UK’s ASTRAEA (autonomous systems technology-related airborne evaluation and assessment) programme has developed and drawn together technologies that will allow unmanned aircraft of any size to fly in all classes of airspace, from high-level controlled air lanes to uncontrolled general air space without any special restrictions. The ASTRAEA consortium brings together companies that have, to date, invested more than £30 million in the project, with the Technology Strategy Board providing additional match funding. The seven companies involved are Airbus, AOS, BAE Systems, Cobham, QinetiQ, Rolls- Royce and Thales.

    ASTRAEA has operated as a major systems engineering programme, split into four broad areas:

  • Autonomy and decision-making – covering how and when a UAV can govern its own actions, how it might manage complex manoeuvres such as pilotless airto- air refuelling, and how it could monitor the health of its onboard systems and carry out in-flight repairs, and how it improves its energy management.
  • Human-machine interface – how to manage the interface between the ground-based pilot and the aircraft.
  • Communications networks – how to maintain links with aircraft that might be flying thousands of kilometres from the operator, and ways of keeping those links secure to prevent unauthorised interference.
  • Detect-and-avoid – providing the ability to ‘see’ and avoid other airspace users ranging from aircraft to parachutists.
  • The first phase researched 12 technology and regulatory topics – see ASTRAEA’s tasks. This phase culminated in a full-scale simulation of two typical missions: a search and rescue mission over Snowdonia and a freight flight from southwest Wales to Inverness. This helped the partners to understand the complexity of the task from planning the mission to shutting down the engine at the end of the flight. It also enabled an early understanding of the interaction with other airspace users and air traffic control. Supported by the UK Civil Aviation Authority, this work involved some 100 companies and universities.

    The second phase of the programme moved into demonstration of the key subsystems and enabling technologies. This included numerous flights using surrogate aircraft to explore and test collision avoidance systems both for other airspace users and for adverse weather and also small UAVs, flying from the West Wales UAV Centre, to simulate security missions in support of a major sporting event.


  • Ground operations and human systems interaction – investigating the technologies and procedures that will be required on the ground
  • Communications and air traffic control – examining what data a UAV will need to send and receive and establishing the case for release of radio spectrum
  • UAV handling – researching the technologies required for autonomous manoeuvring both on the ground and in the air
  • Adaptive routing – developing the technology to enable the aircraft to modify its own flight path and adapt its route in response to a variety of threatening situations
  • Collision avoidance systems – comparing the merits of technologies and systems capabilities that could be used by the UAV for collision avoidance
  • Multiple air vehicle integration – researching technology, procedures and protocols to enable formations of multiple aircraft, both manned and unmanned
  • Prognosis and health management – providing technology and systems to enable the UAV to monitor its own state and how best to maintain optimal mission performance
  • Decision modelling – developing a robust and certifiable system that will provide an onboard decision-making capability replicating all the reasoning functions of the pilot
  • Good airmanship – assessing acceptable levels of UAV ‘good airmanship’ to ensure adequate safety levels
  • Route to compliance – investigation of the means of achieving clearance of UAV system designs
  • UAV operations and procedures – developing a framework for UAV operations with reference to current manned aircraft rules
  • Integration with the operating environment – analysing the issues of integration of UAVs into the existing and emerging air traffic control infrastructure.

    It is envisaged that for all UAVs, a human pilot will always be ultimately responsible for the safe conduct of the flight. With the pilot remote from the aircraft, however, the air vehicle will itself have to take on some responsibilities. The pilot of a modern commercial aircraft can use both intuitive and primary sensing – such as seeing, hearing, feeling and smelling – to generate informed reactions. The pilot also has access to a huge amount of information from cockpit display systems. An unmanned aircraft not only has to replicate the pilot’s own senses but must also encode all of this information in a form suitable for sending down to the ground pilot.

    Video images are analysed to identify clouds and hazardous weather conditions. The system judges the distance to the object in order to take avoiding action © BAE Systems

    If a UAV needs to conduct an emergency landing, the navigation system will look for suitable sites. Using video and infrared cameras, it will check that there is nothing obstructing a landing by identifying the thermal signatures from people, animals or vehicles © BAE Systems

    One area of technology in which ASTRAEA has made good progress is with ‘detect-andavoid’. This is the unmanned aircraft’s equivalent of how the pilot of a manned aircraft avoids other air traffic, the ground, obstacles and dangerous weather. There are many ways of achieving this, but for routine operations the systems must also be interoperable and compatible with the avoidance and separation assurance aids carried by airlines, such as traffic collision avoidance systems. Detect-and-avoid systems must also replicate the pilot’s vision.

    Simple aircraft-mounted video cameras, linked to extensive algorithm sets, have been demonstrated to match a pilot’s ability. They can detect small unidentified aircraft or other objects that are not equipped with traffic collision avoidance systems, even when they appear against difficult backgrounds, such as urban conurbations.

    Improvements in optical processing techniques owe much to the work being undertaken in adjacent sectors such as mobile phone development and gaming. The ASTRAEA partners have undertaken extensive flight trials to verify fused sensing performance using numerous encounter scenarios. The detect-and-avoid performance results have been further optimised in the laboratory, and a prototype system is currently being reconfigured for installation and test within a UAV.

    The priority with this technology is to ensure that the equipment is not oversensitive and does not trigger an unmanageable number of false alarms – see DETECT-AND-AVOID

    The technical challenge for the detect-and-avoid system is to replicate the pilot’s ability to visually scan the scene around the aircraft, decide if there is a risk of collision with another aircraft, parachutist or other obstacle and, if necessary, to instigate an avoidance manoeuvre.

    Detect-and-avoid cameras fitted in the nose of a Metroliner Flying Test Bed aircraft. This non-cooperative system relies on electrical-optical sensors – video cameras – to spot aircraft on a potential collision course quickly enough to undertake evasive manoeuvres. This has to be achieved against complex terrain or urban backgrounds where there is significant potential for numerous false alarm

    In controlled airspace, the air traffic controller will ensure this safe separation and the system will only operate in case of failures. In uncontrolled airspace, the aircraft will advise the ground-based pilot of the potential for a collision and if, through loss of the data link or other reasons, it fails to receive instructions from the pilot, the aircraft will undertake, autonomously, its own collision avoidance manoeuvre. The detect-and-avoid system architecture implemented by ASTRAEA can be described using a modified observe, orientate, decide, act, inform (OODA or Boyd Control) loop based on a number of principal stages:

  • Observe: to use (one or a number of ) sensing techniques to detect and roughly classify all potential threats around the UAV or its intended flight path
  • Orientate: to produce a concise and informed situation picture around the UAV
  • Decide: to determine which potential threats must be responded to, and plan appropriate responses (manoeuvres or path changes, depending on the urgency of the threat) to them
  • Act: to implement avoidance manoeuvres in response to valid threats with air traffic control permission if necessary
  • Inform: to convey the appropriate level of situational awareness and threat pictures to the UAV pilot and record exceptional data for subsequent analysis.
  • Extensive algorithm sets have been developed to ensure sensor output is processed, fused and optimised to present a complete data set to the avoidance (ie decide) function. This in turn recommends the most appropriate manoeuvres to be authorised by the UAV pilot and implemented by the flight management system.


    ASTRAEA has also made good progress in a second key area – communications networks. The networks need to maintain links reliably with unmanned aircraft that might be flying at high speeds, many thousands of kilometres from the ground-based pilot. These links need to be secure and fast, with as little latency (the time-lag caused when signals travel long distances) as possible to ensure rapid decisions and reactions.

    An obvious solution would be to use a satellite-based radio communications network to link the ground-based pilot, air traffic control and the unmanned aircraft. This is not a complete solution, as the limitations of the amount of data that can be handled through satellite links and signal-path delays could compromise safety. A lapse of just a few seconds is unacceptable, particularly in areas of high-density air traffic such as on the approaches to Heathrow Airport.

    A solution that the project is developing is ad-hoc networking. This exploits the communications equipment on other aircraft, manned and unmanned, that are within radio line of sight to create a large, connected airborne communication network. These feature security measures such as encryption to both incoming and outgoing messages. Provided the project can prove that ad-hoc networking achieves the required communications performance, it could prove ideal in ensuring safe flight – particularly in the management of switchovers when one link has to be exchanged for another when aircraft move out of radio line of sight. This development could offer quick, inexpensive and robust communications between UAVs, air traffic control and their ground-based pilots.

    The command and control (C2) link between the ground-based pilot and the air vehicle sends instructions from the pilot to a vehicle and relates vehicle position and health information to the pilot. This link has to be ultra-secure to prevent any external interference. On the other hand, the commands from air traffic control, which will normally be relayed via the aircraft, have to be ‘open’ so that other pilots can listen in.

    In addition to allowing a remote pilot to manipulate the aircraft controls, the C2 link also provides system status and sensory feedback to the pilot. Critical feedback that an onboard pilot would take for granted includes:

  • abnormal ‘feel’ of an aircraft’s response to control inputs
  • detection of turbulence or unusual vibrations
  • detection of unusual noises such as engine stall, bird strike or lightning strike
  • detection of smells, such as smoke, burning
  • visual inspection of wings and engine and other components
  • the view out of the cockpit.
  • The first flight demonstrating how an unmanned aircraft can operate in all UK airspace took place in April 2013. The adapted Jetstream airliner successfully completed a 500- mile trip from Warton, Lancashire to Inverness, Scotland under the command of a ground-based pilot and control of NATS

    While it might be possible to replicate the experience of an onboard pilot to provide a ‘virtual presence’ for a remote pilot, the amount of data would quickly overload the C2 link. The command and control modes for manned aircraft have developed over many years to suit the situation awareness of an onboard pilot. Simply replicating these without replicating the full sensory inputs could lead to unsafe conditions.

    An alternative approach is to increase the autonomy of the aircraft. For example, changing the manoeuvring and flight path control interface from stick, pedals and throttle to autopilot or ‘fly-by-mouse’ could reduce the reliance on real-time sensory feedback, and therefore the dependency on the C2 link.

    This approach could be extended further to provide a ‘goal’-based interface where the remote pilot defines the goal, for example ‘recover to a defined location’, leaving the onboard systems to plan and execute the flight, taking into account the latest available information (such as weather, airfield status and fuel) just as a pilot would. This principle can be applied across all pilot tasks, allowing authority to be delegated to the onboard systems.

    The chosen approach is to vary the UAV’s autonomy, its ability to act independently of the pilot, as the circumstances change – see PACT LEVELS

    Autonomy levels may be characterised by the interaction between the remote pilot and the system, as defined ultimately by the level of authority that the system has to act independently of the remote pilot. A suitable framework for defining different levels of interaction and divisions of authority is the PACT (Pilot Authorisation and Control of Tasks) framework. At PACT level 0 the pilot has full authority, and at PACT level 5 the machine / system has full authority with pilot interaction raised to a supervisory / interrupt level. In between there are various ‘assisted’ levels that, for example, allow the pilot to approve or veto system decisions or proposed actions


    Industries involved in UAV development have seen the certification of unmanned aircraft as a ‘Catch-22’ problem. They have wanted to see the regulations before they developed products, while the regulators wanted to see the products before they gave any commitment to certification. To overcome this potential impasse, the ASTRAEA programme created a ‘Virtual Certification’ process.

    This took a well-understood commercial aircraft, a Jetstream 31, which was fully certified to the European Certification Standard for this size of aircraft. Using technologies developed in the programme, ASTRAEA ‘virtually’ modified the Jetstream 31 into an unmanned aircraft. Then, where required, the project amended the Jetstream’s certification documents to introduce any new or modified systems that would be necessary to render it unmanned. ASTRAEA submitted these documents to the UK Civil Aviation Authority for review and comment.

    The possible uses for small unmanned aircraft are likely to expand rapidly, particularly when their operating range is extended. After a tentative start, there has been a rapid increase in licence applications for UAVs in the UK. Some 200 organisations are now licensed to work with UAVs, in broadcasting, estate agencies, civil engineering, farming, oil and gas monitoring as well as by the police and fire services.

    However, the regulators will require them to carry many of the systems required for larger aircraft if they are to fly beyond the line of sight of the ground pilot. The delivery of takeaway meals or books in crowded urban environments may be a challenge too demanding for the near future. A hub-to-hub concept may be more achievable. For example, the rapid airborne delivery of transplant organs or blood supplies between hospitals may well be realistic within the next five years.


    ASTRAEA typifies the determination worldwide to see the commercial application of large unmanned aircraft early in the next decade. Although this can be seen as a race to exploitation, nations also need to harmonise standards and regulations that can free up the market and avoid constraining operations to within national boundaries.

    Agricultural monitoring. Project URSULA (Unmanned aerial vehicle Remote Sensing for Use in Land Applications) was launched in 2011 and is supported by the Welsh Assembly. The research and development programme has explored the potential for advanced remote sensing, using small unmanned aircraft (pictured), for use in land applications, primarily arable farming. Using input from UAVs, satellites and planes allows precision mapping and analysis down to a plant level © Callen-Lenz Associates Limited

    Several international research programmes are looking at specific aspects of the technologies necessary to achieve this, such as the European Defence Agency MIDCAS programme into collision avoidance. The US has recently designated six UAV test sites to encourage developments, similar to the one developed by the UK’s West Wales Airport. However, ASTRAEA may well be the only programme addressing a total system solution.

    Unmanned aircraft and their new autonomous systems introduce additional legal, social and ethical challenges that have been addressed in Ingenia – see Are we ready for autonomous systems? Ingenia 45. Professional legal institutions are now establishing ‘communities of interest’ to explore the legal liability issues resulting from the repositioning of the pilot to a remote ‘flight deck’ and the transfer of some authority to the machine.

    An effective way is also needed to engage with the wider public – to better understand and address their concerns. The UK government has already taken an initial step by establishing a Cross Government Working Group on Remotely Piloted Air Systems, jointly chaired by the Department for Transport and the Ministry of Defence and including all other relevant ministries.


    UAVs are already being used for farming and environmental monitoring. Soon, there will be surveillance and search and rescue, available for monitoring flooding and forest fires, crop spraying, pipeline protection – all the repetitive asset-management missions.

    Unmanned aircraft will deliver the next revolution in aerospace and create a new market for aerospace products and services. With lower barriers to entry at the smaller end of the market, UAVs will also offer opportunities for new players.

    There is much media hype about the directions and potential of UAVs, but until the technology has matured to a level that will satisfy the regulators, none of these will be allowed to progress in the UK.

    The experience gained by ASTRAEA in developing the technologies and regulations for applications will undoubtedly flow into other sectors as the use of autonomous systems spreads. Progress towards unmanned aircraft will bring benefits to manned aviation in priority areas such as safety, efficiency and environmental performance. For instance, the detect-and-avoid systems developed for UAVs will be an effective pilot aid, particularly for general aviation aircraft. Research into power management to enhance aircraft endurance would also have potential in reducing their environmental impact.

    The UK currently has the world’s secondlargest aerospace industry, generating £24 billion a year in revenue and employing over 100,000 skilled professionals. The ASTRAEA collaboration between government and industry has put the UK in a strong position to capitalise on this new market and to sustain its eminence in the advanced aerospace technologies.

    The next stage for the ASTRAEA project will be to assemble the evidence, through extensive flight trials, which will satisfy the regulators and the public that UAVs can safely coexist in our airspace with manned aircraft.


    Lambert Dopping-Hepenstal FREng is the Programme Director for ASTRAEA. He worked for BAE Systems and its predecessor companies for 41 years, retiring in 2013. As a systems design engineer he has worked on the Hawk, Sea Harrier and Harrier II aircraft before running the Military Aircraft research programmes. Following the formation of BAE Systems, he was appointed corporate Technology Director.

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