The UUAM operations will require a separate, newly created airspace with a new set of rules and standards. Integrating them with the current ATC system will be very complex and is unlikely.
Unmanned Urban Air Mobility (UUAM) is the next happening thing in civil aviation. UUAM is the future mode of transport offering aerial passenger transport within or between cities. Advances in unmanned aerial systems, battery and electric propulsion technology are the main factors that have facilitated UUAM. It is thus possible to use unmanned aerial vehicles that can take-off and land vertically (VTOL) for intra-urban passenger transportation. Many companies are developing the next generation VTOL vehicles. Passenger acceptance and potential passengers’ value of time, are the two key factors for going ahead. The UUAM vehicle could either be rotary-wing, fixed-wing or hybrid cruise vehicles. There is the need to understand the landscape of relevant questions surrounding the implementation of UUAM. The urban airspace would have to look at safety-related factors, social factors, system factors, and aircraft factors.
The fact that unmanned aerial vehicles (UAV) have been successfully flying since 1970s, and the safety record has been continuously improving, has given confidence for UUAM. Removing pilots dramatically increases payload and reduces labour costs. Meanwhile, the advances in civil aviation have seen the boom in less expensive civil travel and light personal jets since the 1990s. Well managed airlines have pulled ahead of the pack. Now as the world begins to reach inflection point, there are signs of hot competition over UUAM aircraft, too. UUAM evolved from the Advanced Air Mobility (AAM), a joint initiative of the FAA, NASA, and the industry to develop an air transportation system that moves passengers and cargo with new electric (i.e. green) air vehicles in various geographies previously under-served by traditional aviation. Nearly 150 companies worldwide are in the race with under-testing UUAM prototypes, to make aircraft not just flyable, but viable. The controllers initially designed for small UAVs were not robust enough for passenger flights. Advances in Artificial Intelligence (AI) are greatly supporting UUAM.
The public is still sceptical. A survey by Booz Allen Hamilton for NASA found that only 21 per cent of people would feel comfortable flying alone in an automated aircraft – though that number increased to 40 per cent if they were accompanied by other passengers that they knew. Two factors should increase public acceptance: the advent of self-driving cars and trucks, and the introduction of rugged, accurate flight systems.
ELECTRIC AND HYBRID PROPULSION
The use of electric motors in multi-rotor designs for “lift-and-cruise” including use of fixed/tilt wings are evolving. Electric motors are coming from the experience of automotive industry. Hybrid-electric turbo-generator are being combined with rugged turbine engines fed by conventional or bio-derived jet fuel that power motors or high-capacity batteries. Energy efficiency - the endurance of batteries will be an issue for UUAM. More efficient rotors, use of lightweight materials, would support minimal energy consumption. Efficiency is better at lower altitudes but it clashes with noise pollution.
THE ELECTROMECHANICAL ACTUATORS
The electromechanical actuators are key to the design of UUAM vehicles. UUAM aircraft will fly low, through thermals and the unusual winds caused by buildings. They must make pinpoint landings dozens of times a day, requiring dramatic power changes and fly-by-wire computers that make hundreds of tiny adjustments every second. The aircraft’s actuators must perform millions of these movements, withstand the unusual vibrations caused by multiple rotors, and be impervious to bad weather, all while maintaining the highest degrees of precision and reliability.
BROADER UUAM SAFETY ISSUES
Unlike a traditional helicopter, new air vehicles use multiple motors and propellers, electric engines, and lighter materials, which make them cheaper, quieter, and more efficient. The operations are expected to cover both urban and rural regions. The operators will compete for the same limited space, which will push the industry to adopt smaller separation standards. For this reason, several agencies are developing frameworks for managing urban airspace and ensuring safety. The safety record and acceptable risk models for hobby drones were clearly unacceptable. The leading UUAM companies are looking to install true fly-by-wire computers derived from airliners, but as small as hardcover book. All these will have a triplex architecture for equalising inputs and commands.
While, UUAM vehicles will have to have more degrees of freedom, they can freely choose their position, altitude, heading, and speed, which increases airspace capacity and reduce flying costs. However, these concepts require high technological capabilities, such as dynamic geofences and advanced sense-and-avoid capabilities, to maintain the required safety levels. Some such features already exist in drone swarms. Collision avoidance algorithms, avoidance maps, and path-planning would be required.
SEVERAL AGENCIES ARE DEVELOPING FRAMEWORKS FOR MANAGING URBAN AIRSPACE AND ENSURING SAFETY. ALSO, ACCURATE WEATHER FORECASTS ARE CRITICAL TO UUAM SAFETY AND ROUTE PLANNING.
Most UUAM companies are currently flying their prototypes at small airports or over remote test ranges. Once they are brought into urban environment, collision avoidance technologies will become critically important. Very compact traffic collision avoidance system and enhanced ground proximity warning system made up of multiple electronic beams using a small phased array are under testing. Safety considerations would also mean avoiding collisions with buildings. Buildings are then the “no-fly” zones where flying is, understandably, prohibited.
WEATHER RELATED ISSUES
Urban canyons and tall buildings also create wind gusts with significant levels of turbulence in their proximity that can cause loss of control and overcome the aircraft’s ability to maintain position, altitude, and stability. Even the autopilot can “overcorrect” and deviate from the planned path which can cause a collision. Precipitation can increase resistance to the movement of aircraft and cause the malfunction of on-board electronics. Low temperatures can decrease battery life. Icing can build up on airframes or propellers and increase the weight of the drone. Visibility and low ceiling could reduce the effectiveness of sense-and-avoid avionics. Weather risks can be reduced by creating dynamic geofences that move with the weather. Accurate forecasts are critical to UUAM safety and route planning.
UUAM CERTIFICATION CHALLENGES
The UUAM certification and regulations has to be managed in many countries with different public and governmental acceptance and understanding levels. Firstly, there are UUAM transportation policy related issues. While certification guidelines have been evolved, yet certification and regulation still require further development.
The current UAVs and drones in use for recreation, traffic monitoring, disaster monitoring, fire detection, infrastructure inspection, mapping, forestry, and agriculture are also increasing in numbers. These operations, although numerous, are currently contained within specific geographic regions and still do not pose a substantial risk or management challenges as will happen with UUAM.
Accommodating exponentially growing UUAM traffic will require innovative solutions in air traffic management, communication, navigation, and surveillance. Creating this for use in urban airspace is not going to be easy, considering the differences in air vehicle designs and sizes, manoeuvrability, speed, take-off procedures, automation, surveillance, and communication capabilities. Clearly, the current air traffic management (ATM) system is not designed to manage urban airspace. Several challenges include higher numbers, greater density, lower altitudes of operations, and varying performance.
The operating environment, rules of air, routes, and integrated scheduling model would have to be evolved. Adaptive control and coordination would ensure efficiency and safety of operation. The much increased flight density and volume would require management.
Integrating UUAM operations with the current ATC system will be very complex and is unlikely. The role of the traffic management system is to segment the airspace, set up the geofences, and approve flight paths within predefined time slots in a first-come-first-serve fashion. The UUAM operations will require a separate, newly created airspace with a new set of rules and standards. The main challenges in air traffic management are airspace integration, separation, contingency management, capacity, traffic flow management, and scheduling. One approach would be through automated traffic and collision avoidance with technologically able to accommodate aircraft of all levels of performance. The operations will not be managed by air traffic control. The routes will be based on social factors.
THERE WILL BE NEED TO DESIGN OPERATIONAL STRUCTURE FOR TERMINAL AREA OF MULTI-VERTIPORT FOR UUAM. MAINTENANCE AND BATTERY MANAGEMENT WOULD HAVE TO BE FACTORED.
The low-altitude airspace is defined as airspace below 400 ft, where the Unmanned Aircraft System Traffic Management (UTM) operations are segregated from other airspace users. FAA has issued clear guidelines for this. The development of UTM is sequenced in four Technical Capability Levels, with the simple, remote, and rural operations in the first phase, and dense urban operations in the fourth phase.
Separate corridors would have to be created. Within the corridors, separation is maintained by UUAM operators and technology. Initially, the corridors will connect two UUAM aerodromes to support point-to-point operations. Later more complex and efficient networks can evolve. Defining two-way traffic lanes that are horizontally and vertically separated would be the way. Certain rooftops will be designated for take-off and landing, while the air in the vicinity of these rooftops is reserved for the climb and descend.
Ground infrastructure for UUAM operations will have to be created. There are issues related to the interaction with existing transport systems. There will be need to design operational structure for terminal area of multi-vertiport for UUAM. Maintenance and battery management would have to be factored.
The concept of multi-ring structure and the junction control, including cooperative scheduling of approach and departure flights, and large flight-flow would have to be worked out. Identified potential sites for building stations based on estimated air taxi demand. The proposed UUAM concepts require extensive ground infrastructures, such as take-off and landing pads and communication, navigation, and surveillance infrastructure. Urban planning, including issues around zoning, air rights, public transportation, real estate development, public acceptance, and access inequalities. Air taxis would initially need aviation ridesharing services.
Technologies such as LTE and 5G-and-beyond cellular services, as well as satellite links will be required to facilitate communication between aircraft and ground points. Accurate GPS availability will be crucial. Battery and hybrid fuel cell technologies are also crucial. Lighter yet stronger materials are important.
UUAM operations will most likely occur at lower flight levels and closer to residential neighbourhoods. Communities are concerned about security, privacy, liability, noise, visual pollution, and air pollution. UUAM noise will cause a significant level of annoyance. Listener’s annoyance is related not only to volume but also to the frequency of sound. It will affect sleep. Stricter standards will be required for building quieter air vehicles or setting up flying routes that reduce noise exposure. Low-level flights might be visually undesirable and disturbing. They clutter the visual field and create shadows. Issues of privacy are exacerbated in residential and business areas. Privacy could relate to behaviour, action, communication, data, image, or location. Drone equipped with cameras can capture images that impact privacy.
PUBLIC ACCEPTANCE AND ECONOMICS
The starting point for the UUAM success would be public acceptance and user adoption. Literature indicates that people, in general, have positive attitudes towards innovation and new technology. However, complex factors determine their willingness and speed in acceptance. Cost of transportation and ticketing will be the next issue. Time-cost trade-offs against on-road travel limits. Then there is the possible market structures.
The idea of UUAM, coupled with the technological development in automation and electricity storage, has spurred growth in the urban aviation industry. The UUAM is in the “honeymoon” phase. New aircraft prototypes are here, and the industry is enthusiastic. There are issues related to technology, regulation, and public conversation. Most commercial airports are currently located in the suburbs, whereas vertiports will mostly be located in more densely populated areas. NASA, the FAA, including India’s DGCA are actively involved. Big players in UUAM include, Amazon, Boeing, Airbus, Embraer-X, Uber Elevate, SESAR U-Space (EU), DLR U-Space (Germany), UTFC, MITRE, METROPOLIS, ONERA, and Singapore UTM, among others. Maximising safety and capacity after understanding technological complexity, noise, and privacy is the essence. India would have to learn from the different urban airspace concepts proposed around the world.