Urban air mobility (UAM) can solve a myriad of transportation problems. This new technology, including electric vertical takeoff and landing (eVTOL) aircraft, promises many benefits, such as reduced commuting times and urban congestion, and may introduce entirely new methods of transportation within and between cities in the coming decade. Commercially-operating eVTOLs are anticipated as soon as 2022 or 2023.
Still, achieving success with UAM is a challenge with a number of technological, infrastructural and legal hurdles. While the most visible activities are vehicle projects, the realization of UAM requires breakthroughs in airspace operations, regulation, and community integration. However, it also creates new and complex safety challenges for the Federal Aviation Administration (FAA)’s aircraft certification process.
NASA AAM Project National Campaign
NASA views the term “Advanced Air Mobility,” or AAM, to encompass developing and deploying aviation in transformative and innovative manners in order to provide aerial mobility in ways not typically seen today.
NASA’s vision for AAM is that it:
- Is safe, sustainable, accessible, and affordable aviation for transformational local and intraregional missions.
- Includes the transportation passengers and cargo as well as aerial work missions, such as infrastructure inspection or search and rescue operations.
- Includes local missions of about 50-mile radius in rural or urban areas, and intraregional missions of up to a few hundred miles that occur between urban areas, between rural areas, or between rural and urban areas
To help make AAM a reality for the United States, NASA will begin hosting a series of activities called the AAM National Campaign in 2022.
The AAM National Campaign series is designed to:
- Promote public confidence in AAM safety.
- Give prospective vehicle manufacturers and operators, as well as prospective airspace service providers, insights into the evolving regulatory and operational environment.
- Facilitate community-wide learning while capturing the public’s imagination.
The AAM National Campaign will bring together aircraft manufacturers and airspace service providers to identify maturity levels for vehicle performance, safety assurance, airspace interoperability, etc., and to develop and demonstrate integrated solutions for civil use.
Working with industry partners, NASA will develop testing scenarios that:
- Address key safety and integration barriers across AAM vehicle and airspace systems.
- Emphasize critical operational challenges towards commercial viability and public confidence in AAM operations.
- Identify requirements for AAM system development.
Important to the future success of the AAM National Campaign is the close collaboration and involvement of the Federal Aviation Administration (FAA). NASA has already been working closely with the FAA and intends to continue teaming with them throughout all stages of the AAM National Campaign. NASA plans to address information requirements and provide lessons learned to inform FAA policy decisions on AAM safety, certification, operations, and airspace integration.
Regulatory Landscape for eVTOLs
For eVTOLs to be deployed commercially at scale, three core aviation regulatory approvals will be required in most jurisdictions: type certification, production certification, and operational authorities. Type certifications are the regulatory approval of the airworthiness of a particular manufacturing design (type design), and are the first step for commercialization of any eVTOL. Many companies are currently in this phase of their business plans, as they design their eVTOL aircraft and pursue a type certificate.
To address eVTOL type certification, the FAA applies one of two existing certification processes in 14 C.F.R. Part 21.17(a) and (b). Part 21.17 (a) involves the designation of applicable airworthiness standards when the aircraft closely matches the characteristics of a particular airplane or rotorcraft class, along with special conditions to address any differences. Part 21.17(b) is used for special classes of aircraft, and the FAA will apply airworthiness requirements derived from other regulations as appropriate, in addition to other airworthiness criteria that the FAA may find to provide an equivalent level of safety to existing airworthiness requirements.
Production certification will allow mass production of a particular eVTOL and is granted when a manufacturer can demonstrate that it can produce aircraft that will meet the standards of a type certificate.
Finally, to operate eVTOLs commercially by transporting passengers or cargo, additional operational requirements and authorizations for commercial operations are required.
Companies wishing to operate eVTOLs commercially must also obtain an Air Carrier Certificate from the FAA under 14 C.F.R. Part 135, which carries additional safety, maintenance, performance, and operational requirements. eVTOL operators must also obtain economic authority from the DOT to operate commercially and will be subject to associated US ownership and control requirements.
In contrast to the approach adopted by the FAA in relying on existing regulations, EASA is developing draft regulations and a new eVTOL certification framework through a series of key building blocks. The result will be a new set of rules, with incorporation of existing regulations where possible.
Air traffic is also much more heavily regulated than road traffic, meaning that policies and regulations need to be ironed out and tested before this type of transportation can be safely opened to the public. The FAA is working to keep pace with the industry by writing regulations as technology is being developed. In July 2020, the FAA NextGen office released a Concept of Operations for UAM aircraft that focused on aircraft operating in corridors.
FAA is currently reviewing applications for certifying eVTOL aircraft, using existing Federal Aviation Regulations for aircraft certification. However, these regulations are still primarily intended for traditional small aircraft with a pilot onboard, whereas eVTOL aircraft may be entirely autonomous. Additionally, UAM aircraft include new technology and novel systems compared to current small aircraft, requiring additional scrutiny during the certification process.
The initial UAM ecosystem will use existing helicopter infrastructure such as routes, helipads, and Air Traffic Control (ATC) services, where practicable given the aircraft characteristics. Looking toward the future, the FAA is working to identify infrastructure design needs for these aircraft. FAA expects to develop a new vertiport standard in the coming years.
Under DO-178C, UAM software testing focuses upon the following four areas in priority and sequential order:
- Functional software requirements-based testing of High-Level Requirements and Low-Level Requirements.
- Normal range testing, which ensures your functional software requirements were complete enough to cover all normal range operating conditions.
- Robustness testing including white-box (“Look at and consider the code/design”) testing including error/boundary values, performance/bandwidth, and Worst-Case Execution Time (WCET).
- Structural coverage analysis assessing the degree to which #1, #2, and #3 above covered the software logic, with additional requirements, then tests of those requirements, added until logic coverage is complete (this is almost always performed via automated commercial tools; see below).
UAM testing: Key software safety needs
eVTOL and UAM software testing will need to address the following gaps:
- Safety requirements derived via ARP4761 based safety impact and pilot workload/automation for each phase of flight
(Hint: Take-off and landing are the most risky phases for most onboard equipment).
- Mandatory fully-independent redundancy for critical systems including flight control, batteries/electrification, and thrust (motors and propeller control).
- Structural (logic) coverage based upon more detailed software requirements; see preceding paragraph and use formally qualified tools such as VectorCAST.
- Software design data flow / control flow determinism with coupling analysis.
- Evidence-based software lifecycle phase entry/exit gates for audited transition criteria.
- More rigorous project-specific plans, standards, & checklists
UAM Taking off
However, UAM is now taking off. By some counts, a staggering 700 designs for electric/hybrid-electric flying vehicles are in development, and many are already in the air. It’s global effort of governments, mostly via agency programs and military-aerospace contractors, as well as aerospace corporations, airlines, automakers, corporations, venture capitalists, academia, and individuals. NASA, Boeing, Toyota, Uber, Intel, and the Massachusetts Institute of Technology are all invested, and that’s just a small slice in the U.S. alone.
You can “pre-order” flying cars from Aeromobil (Bratislava, Slovakia) or Jetson Aero (Stockholm, Sweden. The cost of an on-demand ride-share flight, say several industry estimates, could someday be as low as $2/passenger mile, similar to UberX now for ground transport.
Leisure eVTOLs for one or two passengers are the first to reach the market. The ONE from Jetson Aero, a human-sized drone with a joystick, qualifies as an ultralight aircraft so it doesn’t require a pilot’s license. In the U.S. and many other countries, an operator can fly the Jetson ONE only during the day in rural locations, away from airport zones per Federal Aviation Administration (FAA) Part 103 regulations.
While regulations and lack of infrastructure are still a barrier, many eVTOLs designed for the UAM market are conquering them one certification and country at a time. Japanese startup SkyDrive (Tokyo Japan), a spinout from all-volunteer flying vehicle company Cartivator, announced in September its latest model eVTOL for UAM, the SD-05. This fifth-generation flying vehicle, a drone-like, 12-propeller ultralight for the leisure/commuter market, is designed to carry two passengers, one being the pilot, with a cargo capacity of 1100 lb (500 kg) over a range of 31 miles (50 km) at 62 mph.
In March 2022, the Japan Civil Aviation Bureau (JCAB) accepted SkyDrive’s “type certification” application, which leads the way to examining airworthiness, safety standards, and eventually production certification. Similar procedures apply in the U.S. with the FAA.
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