|(Above) Research at NASA Langley Research Center has involved dummies and a test helicopter to test crash forces. Occupant protection measures include rotorcraft seat/harness systems able to withstand downward acceleration forces of as much as 30 g. Photos courtesy of NASA Langley Research Center and Fischer Seats|
Post-crash fires have been a major focus recently of U.S. safety and regulatory officials — and for good reason.
It’s unfortunate that so many helicopters erupt into flames after a crash, robbing occupants lucky enough to survive the initial impact of their chances to escape the wreck. It’s even more infuriating that the technology capable of mitigating these fires has long been mandated by the FAA, but only in helicopters type-certificated after the mid-1990s. That being said, occupants must first survive the impact before they can escape the blaze. Just as the industry has not embraced swifter adoption of crash-resistant fuel systems, it also has lagged in incorporating better crash-survivability measures.
Regulatory loopholes mean only a fraction of the U.S. helicopter fleet is equipped with the latest advances in impact absorption and restraint, rollover protection and structural integrity that help a skilled pilot-in-command achieve a survivable crash landing.
On the heels of studies showing stagnant accident trends despite scientific progress, the FAA has directed manufacturers, operators and associations to address both issues. The agency on Nov. 5, 2015, launched the Rotorcraft Occupant Protection Working Group as a subset of its Aviation Rulemaking Advisory Committee and gave it six months to write a cost-benefits analysis for improving survivability in helicopter crashes. The group — composed mostly of private-industry representatives — will do its work behind closed doors.
R&WI has asked industry what already is being done to improve occupants’ odds during a crash and what challenges the FAA-appointed group might face in raising the regulatory bar.
The science of surviving a vehicular crash has come a long way since the beginnings of the rotorcraft industry. Then, as one source mused, “you could theoretically screw in a garden chair” and meet the crew-seating standards of the day.
Starting in the mid-1980s, the FAA began to update its occupant-protection standards, which are still reflected in the current regulations governing normal and transport category rotorcraft, or Federal Aviation Regulations Parts 27 and 29, respectively.
For the normal category, FAR Part 27.561 establishes minimum inertial load factors that occupant and item restraints, airframe supporting structures and fuselage structures near the internal fuel tanks must be able to withstand to maintain “survivable volume” in an emergency landing.
Part 27.562 establishes the dynamic testing requirements (using 170-lb test dummies) for crew and passenger seat systems.
Part 27.785 establishes design standards for seats, harnesses and related safety components.
Part 29 includes similar requirements for the transport category.
It’s one thing to set higher occupant-protection standards, but another to meet them. State-of-the-art energy-attenuating seats, harnesses and other components already have been incorporated in other industries like fixed-wing transport and automotive racing, but their rotary-wing counterparts must guard against a different sort of crash.
|Airbus Helicopters upgraded the AS350 with newer seats prior to certification. Photo courtesy of Airbus Helicopters|
“When a helicopter comes down during an autorotation, it impacts more vertically,” said Jeff Trang, technology and flight operations VP at Airbus Helicopters, Inc. “So the character of how an aircraft flies results in a different crash profile.”
According to Thomas Feigl of B/E Aerospace, within the rotorcraft industry, “anybody can produce a non-crashworthy seat, but there are only a few companies in the world that are able to fulfill the new requirements.” B/E subsidiary Fischer Seats is one such company, providing OEMs with rotorcraft seat/harness systems able to withstand downward acceleration forces of as much as 30g, well exceeding the 20g load-factor requirement under Part 27.561.
Airbus has selected the Fischer 180/260 H140 model as its pilot/copilot seat for the H145 T2.
The NASA Langley Research Center can help the rotorcraft industry meet higher occupant-protection standards. Located in Hampton, Virginia, the center performs crash testing and research for customers including the FAA, the U.S. Defense Dept., rotorcraft OEMs and anyone else focused on impact biomechanics. Martin Annett, a researcher with the center’s Landing and Impact Research Facility, explained, “We conduct drop testing and crash testing of anywhere from small-scale materials to full-scale, or from dummies and seats to the whole helicopter.”
The facility can lift a helicopter airframe and swing it into a surface, testing it against a combination of horizontal and vertical forces. “It’s a unique facility because we can control the conditions and attitude and impact pretty well using a set of swing cables off of a gantry structure,” Annett said.
In one recent example, NASA crash-tested two Sikorsky Aircraft CH-46 Sea Knight airframes for the FAA, the U.S. Army and Navy and several manufacturers. “The purpose of the test was to put in some forward and vertical velocities in a medium-lift helicopter, so something on the order of 20 troop positions and five crew positions,” said Annett.
The center looked at various seat systems, restraint systems and crash-test dummies in both sideways and forward-facing seating configurations. Then, researchers “swapped out some components of the airframe that were metallic and changed them to composite materials to look at how well they absorbed energy inherently just by crushing underneath the floor.”
He added that, in addition to physical crash tests, Langley can perform simulations and virtual analysis.
Despite the available options, researchers both within and outside the FAA are troubled by just how small a number of U.S. rotorcraft actually incorporate the new occupant-protection standards of Parts 27 and 29. Accident studies conducted within the past 20 years showed that, despite the new rules, there was little change to the survivability rate in U.S. helicopter crashes even decades after the rules came into effect. Pilots still were dying from blunt force trauma and post-crash fires that the FAA deemed preventable by currently available measures. By the end of 2014, the agency estimated that only 10% of U.S. helicopters had complied with the emergency landing requirements enacted 25 years earlier.
“When the FAA published the new crashworthy rules for the fuel tanks, the seats, occupant protection dynamics and other requirements, their expectation at the time was that the manufacturers would start using those rules,” said Trang. “They have, but only on brand-new aircraft because derivative aircraft are still using the old certification basis.”
FAR Part 21, which governs certification procedures, explains how helicopters in use today can be exempt from the new rules. It contains language saying that applications for a new aircraft type certificate or changes made to an existing type certificate must comply only with requirements in place at the time of application. This is good in the sense that a certificate holder need not worry about having to re-certify every time the FAA changes a rule. But it also means aircraft manufacturers can, in theory, continue producing, selling and flying older type-certificated aircraft that fail to meet the latest requirements for occupant protection.
One might ask not how, but why an industry so dependent on safety would resist implementing the best technology. But those familiar with aviation know the answer comes down mostly to economics, or perhaps more specifically to a trio of variables that drive innovation: cost, time and performance. These are the factors the FAA’s working group must weigh before presenting its cost-benefits analysis in May.
Cost is an obvious downside to redesigning helicopter cockpits to a higher standard. “A 30g seat with its energy-absorbing element requires certain technology, and that makes it expensive in design and testing as well as in production,” said Feigl. Even after installation, a more-protective seat system may require higher maintenance costs.
Performance factors make operators wary of any equipment upgrades that add to an aircraft’s basic empty weight. “If we proposed a piece of equipment that weighs only 10 lb, you’d be amazed at how much pushback we will get from some of our customers,” said Trang. “It doesn’t sound like much, but every pound is precious depending on their mission and operating environment.”
But, added Lindsay Cunningham, Airbus Helicopters, Inc.’s aviation safety director, weight really only impacts performance when it comes to crash-resistant fuel tanks (covered separately in FAR 27.952) and other larger items. Energy-attenuating seat systems and associated components are light enough to have negligible impacts.
The industry’s biggest concern, according to Cunningham, might be the time and effort required to certify to new FAA standards.
As we have reported, some in industry view certification with disgust (“Whither Single-Engine IFR?”, “Moving the Mountain,” R&WI, June 2015, pages 22 and 32). Applicants for type and supplemental type certificates often find themselves buried in complex procedures or having to wait months for the resource-strapped agency to process their applications.
“In our industry specifically, a major barrier is a pervasive reticence to tackle the daunting task of certification,” said Carl Schopfer, chief technology officer of MD Helicopters. “With many of the safety improvements necessary to dramatically improve crashworthiness and survivable volume not being mandated across the board, most component and airframe manufacturers are not eager to grapple with the complexities of certification.”
Surprisingly, the industry’s aversion to certification might actually make the problem seem bigger than it is. Cunningham told R&WI that the FAA’s estimate of 10% compliance to the new standards might actually be low and that many more companies have probably met or exceeded the new occupant-protection requirements off the record, avoiding the tedious process of getting them certified to higher standards.
Airbus did so with the AS350 when it replaced the original AStar seats with newer Zodiac Aerospace CS27 Hydro Series, she said. But it has not officially certified it to the latest requirements.
The AStar, introduced in 1975, also technically predates those requirements. “Even though we couldn’t originally certify what we call ‘bucket-style’ seats in there, we voluntarily started installing those,” said Cunningham. “So every aircraft, every B3e for example, in more than the past 10 years has been equipped with the latest standard energy-attenuating seats and crew seats, even though it wasn’t required.”
The FAA’s working group has a lot to consider if it intends to require older but still-active helicopters like the AStar to meet the latest occupant-protection standards. But in the meantime, the tide is slowly changing. New-generation aircraft are coming online, each one possessing cabin and structural features that more than meet FAA requirements.
To meet those standards, Bell Helicopter had to design its new Bell 525 Relentless from the ground up. To preserve a survivable volume during a crash, the 525 airframe structure retains large masses above and behind the occupied volume and includes crew and passenger crashworthy seating systems, according to Bell.
The 525 also incorporates an anti-plow bulkhead to minimize earth or water “scooping” during a longitudinal impact, the company said. The bulkhead connects to the 525’s keel beam and an aluminum post beam that runs up the center of the windshields and supports a wire-strike protection system. Passenger seats in the 525 are each one seat away from an emergency exit, and the seating systems stroke downwardly to absorb vertical kinetic energy at levels below human injury thresholds, the manufacturer said.
Bell claims its military V-280 Valor “has tremendous features” for occupant crash survival. Large masses, such as the engine, transmission and rotor, are separated from the occupied compartment to improve survivability. It said the V-280 design for the wing-fuselage joint to fail in the case of a controlled crash to prevent the combined mass of the wing and nacelles from driving the fuselage into the terrain.”
The members of the FAA Rotorcraft Occupant Protection Working Group are:
Injury Analysis; Safety Research Corp. of America; HAI; General Aviation Manufacturers Assn.; Airborne Law Enforcement Assn.; Survivors Network for Air & Surface Medical Transport; MD Helicopters; Bell Helicopter; Sikorsky Aircraft; Enstrom Helicopter; Airbus Helicopters; Robinson Helicopter; Air Methods; Air Evac Lifeteam; Papillon Airways; PHI Air Medical; Robertson Fuel Systems; Meggitt Polymers & Composites; BAE Systems, and EASA (as a non-voting member).