Standards Up in the Air

More than 100 years after the Wright Brothers took their first flight, ASTM International committees are working to enable technical innovation and keep the skies safer than ever.

One hundred years ago, the possibilities for the fledgling aerospace industry were limitless. Less than 20 years earlier, in 1903, Americans Wilbur and Orville Wright had proven that sustained manned and powered flight was possible. This opened the doors to aircraft production, sales, and military usage. 

Subsequent technical innovations, including the conversion to metal frames, cantilevered wings, and the shift from biplanes to monoplanes further expanded the use of airplanes. By the 1920s, countries around the world began using planes for mail and freight delivery, entertainment in the form of stunt shows, and limited passenger flight.

Now, a century later, aviation has become a driver of global business, an enabler of international trade and tourism, and the fastest worldwide transportation system. Since its inception, aviation/aerospace has seen a steady and significant series of technological advances. Yet more can be seen on the horizon, including autonomous unmanned aircraft systems, electric or hybrid-electric aircraft, and “flying taxis” or eVTOLs (electronic vertical take-off and landing). Guiding the industry on this path of innovation are ASTM International’s aviation committees. 

Foundational Standards for UAS

Among the committees tasked with developing aviation standards is the committee on unmanned aircraft systems (UAS) (F38). According to chair Phil Kenul, the committee continues to develop foundational standards for UAS. 

“Beyond visual line of sight, detect and avoid, UTM [UAS traffic management] — these are the things that will advance the commercialization of the UAS industry. To get into an airspace, you need to have the architecture for that airspace. We’re working very closely with other ASTM aviation committees to get the infrastructure and architecture in place. We believe that our standards will become applicable to aviation in general,” he said.

Currently, the subcommittee on flight operations (F38.02) is revising one of its hallmark standards: the specification for remote identification and tracking (F3411) and developing a means of compliance. Remote ID and tracking allow for government and civil identification of unmanned aircraft systems while still preserving the operational privacy of remote pilots, businesses, and their clients. By increasing UAS remote pilot accountability, UAS can operate over people and beyond visual line of sight (BVLOS). Remote ID applies to an array of UAS types and operators.  

“It was the highest priority of the FAA [U.S. Federal Aviation Authority], and we published the remote ID standard ahead of the final rule at their request. The new rule will be used by FAA, with the standards, to form a basis for expanded operations of small UAS. Now, in the interest of supporting the industry and having a globally harmonized standard, we’re working very closely with the FAA to revise the standard. The revision being developed will ensure compliance with North American and European regulations. It’s one of the most important standards to the industry that we’ve been working on for the last two years,” Kenul said.

Along with remote ID and tracking, the committee is updating the test method for assessing the safety of small unmanned aircraft impacts (F3389). Ultimately, this standard will safeguard against serious or fatal injuries if a UAS should accidentally strike a person. The specification for detect and avoid system performance requirements (F3442) is also undergoing review to ensure that it reflects new capabilities and improvements. 

The UAS committee also recently published the practice for development of a durability and reliability flight demonstration program for low-risk unmanned aircraft systems under FAA oversight (F3478). Created at the behest of the FAA, the standard pertains to flight demonstration plans for low-risk UAS seeking certification from the FAA. These are UAS that have been tested and have proven to be durable and reliable. 

Kenul notes that the certification process for smaller UAS, such as those used in package delivery, is demanding. Unmanned aircraft operating in urban areas must demonstrate more incident-free flight hours than those in rural locations. All UAS must demonstrate that the aircraft is reliable and durable and can be flown safely.

The UAS covered by the standard must also meet the following criteria: possesses a command-and-control link that enables the pilot to take contingency action; has a kinetic energy of ≤25,000 foot-pounds (34 kilojoules) calculated in accordance with methods specified in the means of compliance; operates ≤400 feet (120 m) above ground level; outside of internal combustion engines and fuel cells, is electrically powered; does not operate over open-air assemblies. 

Striking a Balance

ASTM’s strategic advisory committee AC377 falls under the auspices of F38 but includes members from several ASTM aviation committees, including the aircraft systems committee (F39). In 2019, AC377 released “Technical Report (TR) 1, Autonomy Design and Operations and Aviation Terminology and Requirements Framework.” Focusing on certification requirements for autonomous aviation systems, this technical report influenced the proposed practice for exercising a contextual framework for increasingly autonomous aviation systems (WK76044). Drafted by the subcommittee on aircraft systems (F39.04), WK76044 will produce a set of practices aligning with the contextual framework described in TR1. 

“In TR1 we posed a lot of questions, such as, ‘How do you do decompose the functions of the pilot on an aircraft?’” says Andy Lacher, a member of F38 and F39 and WK76044 working group lead. Lacher is also the director of aerospace systems research at Noblis, a nonprofit science and engineering company working for the U.S. federal government. “Now we’re going to provide guidance on how to answer those questions. What we’re looking to do as a community is to help proponents, especially the new entrants in the aviation space, with guidance on balancing safety and new technology. This should provide a means by which proponents do analysis of system requirements related to increasingly autonomous systems in a deliberate, consistent way that hopefully will inform their design and interactions with the regulator. Regulators are interested in that consistency, and a standard practice seems to resonate within the community.”

New standards for alerting methods will help make flying safer.

Safety First and Always

ASTM isn’t focused solely on unmanned systems. The committee on general aviation aircraft (F44) has drafted two proposed standards to improve manned flight safety: the practice for enhanced indication methods in aircraft (WK71556) and the practice for alerting methods in aircraft (WK71557). These documents build on a critical standard: the specification for low-speed flight characteristics of aircraft (F3180). An initiative of the European Aviation Safety Agency (EASA) and FAA, this specification outlines departure characteristics for single- and multi-engine aircraft, stall characteristics, stall warning, spinning, and safety features that assist pilots with a stalled aircraft. 

As outlined in the practice for enhanced indication methods (WK71556), an electronic display shows when the plane is nearing a stall. Certain symbols signify specific stall characteristics and warn the pilot that if he or she doesn’t take immediate action, the plane will reach a stall condition. These indication methods ameliorate the loss of controlled flight and alleviate the risk of inadvertently going into stalls and spins and losing control of the aircraft. 

The practice for alerting methods (WK71557) defines the characteristics of a stall warning system. “If you’re going to receive credit for an oral stall warning, here are the characteristics that the warning system must possess. It must have a unique oral sound — a spoken voice, tone, etc. — that doesn’t sound like anything else in the airplane. If it’s a tactile warning, like a stick shaker or a buzzer, the pilot must be able to feel it even if wearing gloves and if the airplane has other vibrations. If a pilot is busy looking at charts, the alert will get his or her attention right away so the situation can be remedied. The practice really identifies the characteristics of this stall warning alert, and if applicants follow that practice, they receive full credit for stall warning systems that meet F3180,” says Dean Boston, chief certification engineer at Genesys Aerosystems, member of F44, and chair of crew interface task group AC394, a task group in F44.10. 

Also on the general aviation aircraft committee’s docket are electric-powered and hybrid-electric aircraft – and within Part 23 of the FAA’s Title 14 of the Code of Federal Regulations. According to Boston, the original Part 23 did not accommodate these powerplants. The powerplant subcommittee (F44.40) is developing the requirements for the electric propulsion system and electric power distribution. The latter covers how power goes out to the motors compared to how it travels to avionics, radios, and other equipment on the airplane.

Another key area for the committee is airplane systems information security. “The FAA and EASA have raised concerns about, and are working on regulations for, airplane system hacking or disrupting the computers on board an aircraft,” says Boston. “There will be new regulations and advisory circulars for protecting against that kind of event happening. They will determine what protection or cybersecurity measures must be put in place for the computer systems on board the airplane. What we’re doing in F44 is developing the practice for aircraft systems information security protection (WK56374), which will be appropriate for the Part 23 smaller airplane environment as opposed to the larger, transport category Part 25 airplanes. The requirements will be appropriately scaled to the size of the plane and number of passengers.” He also notes that the subcommittee on systems and equipment (F44.50) is working on these requirements. 

Safety revisions are also being made to light sport aircraft standards. To reflect the maximum fuel vapor pressure experienced in the field and to prevent vapor lock, the committee on light sport aircraft (F37) has revised the specification for design and performance of a light sport airplane (WK64937). Committee chair Adam Morrison notes that automotive fuel blends vary widely over the course of the year, changing to accommodate weather conditions and for emissions and environmental concerns. 

“The environment in an aircraft is much more aggressive and, as an aircraft engine gets hot and altitude increases, these fuels can begin to boil and create vapor in the fuel system. This can inhibit fuel flow and lead to a stalled engine or power loss. There are occasional accidents and incidents that can be traced back to fuel vapor lock, and the committee wanted to add some ‘right-sized’ requirements to educate manufacturers and provide a straightforward path to verifying their aircraft systems,” he says. Morrison is also the CEO of the strategic consulting firm Streamline Designs, which works on both manned and unmanned aircraft systems. 

Additionally, F37 is developing standards for the FAA’s Modernization of Special Airworthiness Certification (MOSAIC). This rewrite of light sport aircraft regulations will expand the aircraft category to include new and novel types, such as electric and hybrid-electric propulsion and vertical take-off and landing. The rule may also feature an increased airspeed, a maximum stall speed and horsepower cap, and the possibility of commercial use of light sport aircraft. MOSAIC is currently undergoing internal FAA review, and its anticipated publication date is late 2023.  

Building on the practice for maintenance and the development of maintenance manuals for light sport aircraft (F2483), the subcommittee on cross cutting (F37.70) has crafted the specification for the development of maintenance manuals for light sport aircraft (WK63118). 

“Since the industry has matured over the years, it has become apparent that F2483 needs to be split into two separate standards, one for each of the subjects. It is sometimes confusing for manufacturers and regulators to show compliance with a standard that covers such a broad range. By splitting the standard into two, it will make it clearer that a manufacturer needs to have an internal system for handling maintenance as well as a maintenance manual that gets shared with their external customers,” Morrison said. 

On the Horizon 

As the aviation industry continues to evolve, certain trends have become apparent. One is the move toward automation, which Merriam-Webster defines as “automatically controlled operation of an apparatus, process, or system by mechanical or electronic devices that take the place of human labor.” In aviation, automation reduces the pilot’s workload and fatigue level, improves the performance of routine operations, and increases safety through such features as anti-stall alerts. Although it offers benefits, automation does alter the role of the pilot.

“In the future, pilots may be steering or aiming their aircraft, but they might not be able to have direct command over the flight control surfaces,” says Lacher. “In eVTOL aircraft with unified flight controls, the pilot simply commands it to go up and forward. The aircraft takes off vertically, transitions to horizontal flight, and then returns to vertical flight for landing. With the complexity of the aviation system, we aren’t going to reach autonomous flight in one big leap. The standard practice that F39 is coming up with will be a piece of the answer but not the whole answer,” Lacher said.

eVTOL aircraft may take to the skies as early as 2024. In April, Aviation Today reported that New Zealand has begun testing the use of self-piloted, two-passenger, all-electric aircraft for cargo delivery, hazard management, and agricultural and monitoring services. In the United States, the United Parcel Service plans to test eVTOLs for its Express Air deliveries. If effective, electric vertical aircraft would replace small UPS planes carrying 500 to 3,000 pounds (230 to 1400 kg).

“In terms of electric propulsion and eVOTLs, the industry is moving faster than the standards are,” says Boston. “There are a lot of companies doing the development work without standards. The thrust that I see over the next few years is to get the standards published and get them to the applicants.”

Also arising from the automation trend and the increasing presence and capabilities of UAS is the need for UAS traffic management (UTM). The specification for UAS traffic management UAS service supplier interoperability (WK63418) will go to ballot this spring. Developed by F38 with input from the industry, FAA, NASA, the Swiss civil aviation authority, and others, the proposed standard covers an array of capabilities, such as the integration of manned flights and management of priority flights. The committee is also looking at how UTM architecture could inform the development of traffic management for urban air mobility.

“We are working across sectors to ensure this becomes the foundation for a global UTM standard for managing unmanned traffic in the future,” Kenul says.

Through their new and revised standards, ASTM’s aviation committees are charting the path to aircraft innovation, safety, and reliability. By taking into account technological advances, performance requirements, and safety considerations, they will set the course for the future of manned and unmanned aircraft systems.

Written by: Kathy Hunt, journalist and author, for ASTM.