Crash-Resistant Fuel System Update

New tanks, valves, awareness and pending regulations increase post-crash survivability.

March 6, 2015, an Airbus Helicopters EC130 B4, N356AM, operated by Air Methods Corp., struck the edge of a hospital building and impacted its parking lot near St. Louis, during approach to an elevated rooftop helipad. The helicopter was destroyed by impact forces and a post-crash fire. The pilot was the sole occupant and sustained fatal thermal injuries.

July 3, 2015, an Airbus Helicopters AS350 B3, N390LG, operated by Air Methods Corp., partially impacted a parked recreational vehicle in a parking lot near Summit Medical Center in Frisco, Colorado, after takeoff from a ground-based hospital helipad. The helicopter was destroyed by impact forces and a post-crash fire. Video footage revealed a post-crash fire after ground impact concurrent with large quantities of fuel flowing from the helicopter wreckage.

Neither helicopter was equipped with a crash-resistant fuel system (CRFS), which if installed, may have prevented or reduced the risk of thermal injuries.

Because of the growing awareness raised by fuel-fed incidents like these, the FAA is weighing new proposals for retrofit of crash-resistant fuel systems as an effective safeguard against post-crash fires.

Stopping the Fire

Fires have long been a helicopter hazard because they can erupt after low-impact crashes and/or hard landings that pilots and passengers could survive if they weren’t engulfed in flames or smoke. Uncontained rotorcraft fuel can turn into a mist, which when exposed to an ignition source, produces a fireball.

Understandably, since 1994, the FAA has required that all helicopters certified after 1994 be fitted with crash-resistant tanks and other CRFS components. This is mandated in the crashworthiness requirements of Part 27.952 or 29.952 for normal category rotorcraft.

Unfortunately, the helicopters in the above crashes were certified for production before the 1994 requirement. In fact, because most new helicopters are built according to the old designs, they are also exempt from the safety requirement. “In 2014, a review of newly manufactured helicopters since the introduction of standards for crash-resistant fuel systems found that only 15% of newly manufactured helicopters since 1994 have fuel systems that comply with 14 CFR 27.952 or 29.952, even though these standards were introduced more than 20 years prior,” said Chihoon “Chich” Shin, aerospace engineer of helicopters at NTSB. “The NTSB issued safety recommendation A-15-12 to the FAA to require, for all newly manufactured rotorcraft regardless of the design’s original certificate date, that the fuel system meet the crashworthiness requirements of 14 CFR 27.952 or 29.952.”

The StandardAero/Robertson Fuel Systems tank is listed in the FAA’s list of helicopters with crash-resistant fuel systems.Photo courtesy of Robertson

“The idea that FAA regulations have been in place since 1994, yet are not required in some current production helicopters, is difficult for the general public to understand,” said Bill York, director of engineering at Robertson Fuel Systems. “NTSB recommendations and congressional inquiries have also created interest in CRFS. Operators are becoming more aware of the availability of helicopters with CRFS or the ability to upgrade current fleets with CRFS and pushing forward to upgrade their equipment.”

FAA posted a special airworthiness information bulletin (SAIB) Oct. 13, 2017, alerting owners and operators to the list of helicopters “that are fully compliant with the crash-resistant fuel system safety standards” of Part 27.952 or 29.952. “The airworthiness bulletin is an effective means of advising all owners and operators whose aircraft, which may fall short of compliance with the latest fuel tank crashworthiness standards, that new, certified retrofit CRFT solutions are now available to the market,” said Elvis Moniz, VP of business development for airframes and avionics solutions at StandardAero. “We are happy to note that the FAA was quick to add the StandardAero/Robertson CRFT to the list of approved options.”

Shin believes the bulletin only focuses on rotorcraft that currently meet the standards of Part 27.952 and 29.952, but does not address modifications which may improve fuel system crash resistance. “Ultimately, the SAIB should better inform the public of helicopters, as well as available modifications, that are fully compliant with 14 CFR 27.952 and 29.952.7,” he said.

ROPWG Rescue

Dennis F. Shanahan is chairman of the FAA’s Aviation Rulemaking Advisory Council (ARAC) Rotorcraft Occupant Protection Working Group (ROPWG) and reports directly to the ARAC chairman. The group has spent a year looking at hundreds of helicopter crashes, specifically those that didn’t comply with FAA standards for fuel systems implemented in 1994.

Shin said the advice and reommendations produced by the ROPWG ARAC to the FAA can help spur an increase in the rate at which this important safety technology is incorporated into the civil rotorcraft fleet.

“CRFS are designed to prevent significant fuel leakage in potentially survivable crashes, thus preventing fuel-fed, post-crash fires,” Shanahan said. “OEMs are moving rapidly to incorporate CRFS into currently manufactured helicopters. Several manufacturers offer CRFS retrofit kits for out-of-production helicopters. Operators of out-of-production helicopters without CRFS should consider installing a CRFS retrofit kit if one is available for their helicopters. Hopefully, the ROPWG recommendations will have significant influence on the FAA final decisions on this subject. Some congressional members are monitoring the ROPWG reports on this subject to help inform them on the issues related to their bill.”

A helicopter post-crash fire.Photo courtesy of Lake Dillon Fire Rescue

The working group has already submitted a report to the ARAC, which was approved and submitted to the FAA with most its recommendations. The due date for ROPWG’s next report to the FAA was Jan. 25, 2018. It was to be a final report that will cover both the fuel systems and also the seat and structures. “It won’t become public until ARAC accepts it,” Shanahan said. The next aviation rule-making advisory council meeting is March 15, 2018.

What is this report and what impact will ARAC have? “The committee will surely recognize the potential financial impact of new legislation on helicopter operators as part of their studies,” said Moniz. “[It] will — accordingly — hopefully take into consideration the fact that hundreds of smaller operators could benefit from a relatively straightforward retrofit of an improved fuel container upgrade, using proven, robust, military fuel-restraint technologies.”

Getting Retrofitted

Companies are developing and producing retrofit kits to add CRFS to helicopters that were type certificated prior to the 1994 regulations.

The systems have worked for the U.S. military, which have required them in its rotorcraft since the 1970s. Doing so has reportedly resulted in a 66% reduction in post-crash fires in survivable accidents and an 18% reduction in post-crash fires in nonsurvivable accidents. These systems also resulted in a 75% reduction in thermal injuries and no thermal fatalities in survivable impact conditions. The results of the FAA’s research program and the U.S. Army’s experience demonstrate the importance of ensuring that newly manufactured rotorcraft comply with the current airworthiness standards for crashes.

“The technology for CRFS is mature and well proven in military aircraft,” said Jeff Bracken, VP and chief technology officer at Robertson Fuel Systems. “Adapting the same basic technology to light rotorcraft can be done economically. The most recent example is our STC solution developed with StandardAero, to add a crash resistant fuel tank (CRFT) to the Airbus AS350/EC130 aircraft.”

Robertson hopes CRFS in light rotorcraft becomes part of the expected normal condition for rotorcraft safety in the same way that shoulder belts and airbags have in the auto industry, said Bracken. “It is time to move forward,” he said.

Fuel containment and isolation are the underlying principles of CRFS. Shanahan believes one of the core components to achieve this is a crash-resistant fuel bladder, claiming more than 90% of CRFS effectiveness can be found there. “[The bladder is made of] a composite material that has a great deal of strength and penetration resistance,” he said. “Putting that inside the tank protected by structure on the outside makes it less likely for tanks to be compromised.”

Bracken said that the CRFS bladders incorporate metallic fittings to accommodate protrusions into or out of the bladder. He feels that the keys to crash resistance are bladder-fitting strength and tear-resistance. In the event of a crash, the fuel bladder may try to separate from the fuselage. “The bladder fittings and any attachment to the fuselage need to be robust enough so that the bladder doesn’t tear,” he said.

The StandardAero/Robertson CRFT solution, recently certified for the Airbus AS350/EC130 family, is retrofittable into existing helicopters. Designed with input from operators, it is easily retrofittable with minimal downtime and structural modifications.

A successfully installed crash-resistant fuel tank.Photo courtesy of StandardAero

“The retrofit maximizes crew and passenger safety in all unplanned landing conditions and is easily maintainable, while delivering similar or better performance than the original, dated fuel tank design,” Moniz said. “[It takes] into account penetration threats such as the surrounding structure, cargo hook and flight controls. The container is of a stiffer and lighter carbon glass composite construction than the original OEM design, and incorporates extremely robust fuel bladder technologies. A fuel sump drain valve was relocated and redesigned to prevent inadvertent activation in a hard landing or when landing on deep snow or brush.

“A newly designed crashworthy fuel filler neck and fuel cap also ensures a simple and robust fuel containment system, even in the event that the connection between filler neck and airframe is breached. [It] is compatible with cargo hooks and swings and aftermarket icing filters, and was designed to be easily installed on multiple platforms using the same fuel container. It utilizes existing fuel system support components (e.g. cockpit fuel indicator and fuel tank support beam assembly), minimizing aircraft downtime and installation complexity. This in turn makes it possible for operators to install the kit themselves, or for our field service representatives to undertake the installation on-site at the operator’s base.”

Worldwide Awareness

Rotorcraft CRFS awareness is going global. The systems will appear in Russia next year, and the Ka-226 helicopter will be the first Russian light helicopter equipped with it, said department director of Technodinamika Holding Egor Chetvertnykh. The Ka-226 is a lightweight multirole helicopter with a takeoff weight of 3.4 tons. It is intended to carry up to 1.5 tons of cargo or up to seven passengers on board to a distance of 600 km.

Also, according to Shanahan, the Australian government grounded Robinson Helicopter R-44s until they were retrofitted with CRFS bladders. “Robinson had been working on it, and had the retrofit system and was able to insert the bladder into the tank with the same concept as the military,said Robinson. “Since Robinson made these changes eight years ago, none of the retrofit helicopters have had post-crash fires. By making the change to the tank and the fuel lines, they were able to get exceptional results.”

The industry and certainly the public as a whole hope these exceptional results will continue to derive from rotorcraft crash-resistant fuel systems. RWI

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