Bell and Leonardo bring IFR-capable aircraft to market.
This past summer, our industry welcomed back an old friend, one that hadn’t been seen in the US market since 1999: the single-engine helicopter certificated for flight under IFR conditions (SE-IFR). In July 2019, Leonardo received an FAA supplemental type certificate (STC) for the first SE-IFR helicopter in more than two decades, the TH-119. Less than a month later, Bell received an STC for its 407 GXi to operate under instrument flight rules.
It’s no coincidence that both of these exciting new entrants arrived so recently. These first certifications are the culmination of decades of work behind the scenes, in both technology and regulation. The paths the two manufacturers took to certification, however, are vastly different.
SE-IFR: A History
To truly understand the SE-IFR issue, it’s important to understand how we got here.
Helicopter flight rules for instrument conditions made their first appearance in the 1970s. At the time, single-engine rotorcraft conducted IFR flights regularly, well before the advent of GPS, glass cockpits, and digital autopilot systems. The rules these helicopters were certificated under, found in Appendix B of 14 CFR Part 27, Airworthiness Standards: Normal Category Rotorcraft, hadn’t changed significantly since the early 1980s.
In 1999, the FAA issued AC 27-1B, Certification of Normal Category Rotorcraft. This document, which was a total revision of AC 27-1A, issued in 1997, dictated the extinction of SE-IFR rotorcraft.
AC 27-1B in essence incorporated into Part 27 numerical safety analysis methods as a way of determining OEM compliance in meeting safety standards. The advisory circular (AC) required helicopter manufacturers to prove that critical aircraft systems had an “extremely improbable” failure rate of one in 1 billion. In other words, OEMs had to demonstrate that these systems would incur only one failure in 1 billion hours of runtime. Any critical onboard system that couldn’t meet this failure rate was required to be duplicated, with redundancy providing an additional safety margin.
Overnight, single-engine IFR helicopters became cost and weight prohibitive.
In 2003, AC-1B was revised again, raising the bar even higher. This time, the AC defined loss of function of attitude, airspeed, or barometric altitude instruments, or conditions that would cause those instruments to issue hazardously misleading readings, as individually “catastrophic” when operating in instrument conditions. Industry interpretation of this change was that triple-redundant systems would now be required.
At the same time the 2003 AC was issued, Part 23 single-engine airplane manufacturers received relief from these new requirements: SE-IFR airplanes were required to meet a probability of one in 1 million before being subject to duplicate systems. In response, new aircraft came on the scene, like the Cirrus SR-series, that deployed the latest GPS, glass cockpits, and autopilot technology. This relief wasn’t extended to the helicopter industry, however, in part because the latter was still a long way off from meeting even this lower probability requirement.
“There are several reasons why regulation changes for small light airplanes couldn’t be extended to helicopters at the time,” says Harold Summers, director of flight operations and technical services at HAI. “Helicopters aren’t inherently stable like airplanes. There also was a great deal of work needed to prove that the aircraft could be safely flown in IFR conditions without all the redundancies. The advanced, lighter technology for helicopters hadn’t yet caught up.”
Industry Asks for Change
In 2015, with support from partner associations, the helicopter industry petitioned the FAA to consider reducing certification barriers for SE-IFR helicopters. In the 16 years since the publication of AC 27-1B, a number of important technologies, including WAAS (wide area augmentation systems), GPS, cell phones, tablets, and flight planning apps, had been introduced, all available in affordable, lightweight, consumer-friendly packages. The industry was finally in a position to meet the same one in 1 million standard as light airplanes.
In the summer of 2015, HAI, AHS International (rebranded in 2018 as the Vertical Flight Society, or VFS), the General Aviation Manufacturers Association, and the Aircraft Electronics Association published the 14 CFR 27 Single-Engine IFR Certification Proposal, an association and industry white paper (bit.ly/SE-IFR). The proposal explicitly linked improving helicopter safety to facilitating an economically viable certification plan for SE-IFR helicopters and expanding IFR operations.
The paper referenced worldwide helicopter accidents related to flights in marginal VFR (MVFR) and inadvertent entry into instrument meteorological conditions (IIMC). The authors argued that more accidents (194), and resulting fatalities (326), occurred from 2001 to 2013 from pilots being ill-equipped for MVFR and IIMC conditions than would have occurred from the expected failure rates of SE-IFR helicopter systems.
“The lack of SE-IFR helicopters developed a dangerous culture in our industry,” explains Paul Schaaf, former HAI vice president of operations and the HAI lead for the white paper. “Pilots needed to get their instrument rating to get a job, but very few used it again if they flew single-engine operations. Few companies kept their pilots’ instrument skills strong. Add to that the pressures to get the job done if there’s any chance of VFR, and it’s a recipe for disaster.
“We argued that the probability of IIMC and controlled flight into terrain was higher than any probability of equipment failure,” Schaaf continues. “By allowing SE-IFR helicopters, we could save lives.”
The white paper addressed six key concerns with the FAA’s certification standards for SE-IFR helicopters:
- Use one in 1 million as the failure rate that would require redundant systems in lighter SE helicopters rather than the original FAA standard rate of one in 1 billion
- Allow generic high-intensity radiated field (HIRF) testing based on established construction techniques (ambiguities in the then-current Part 27 language required testing on a case-by-case basis each time a new piece of equipment was added)
- Allow a single hydraulic system when aircraft can be shown through rigorous testing to be flyable without hydraulics
- Reduce the requirement for three navigation communication systems to two
- Reduce the requirement for dual pitot–static systems to one
- Allow a battery to be considered as a second electrical generation system.
In 2017, the FAA released policy statement PS-ASW-27-15, Safety Continuum for Part 27 Normal Category Rotorcraft Systems and Equipment, which adopted some of the processes and concepts recommended in the white paper. With the publication of the Safety Continuum, the FAA officially recognized that safety and risk must be balanced across a wide spectrum of aircraft and operations, specifically calling out aircraft weight and propulsion type, whether passengers are flown for hire, and societal expectations as major factors in airworthiness decisions.
The FAA saw the Safety Continuum as a way to “facilitate a more rapid incorporation of advances in technology for systems and equipment by recognizing a balanced approach between the risk and safety benefits [of] installing such technology.”
Through the FAA’s Safety Continuum process, helicopter manufacturers received relief in failure probabilities and can now request waivers from the AC 27-1B requirements by submitting issue papers. After close review, the FAA can decide whether to issue the waivers.