Airbags going airborne, without the hot air

 - March 22, 2007, 9:32 AM

Contrary to a popular misconception, most aircraft accidents are survivable. This fact has been documented by the NTSB, which analyzed Part 121 accidents in the U.S. between 1983 and 2000 involving at least one fatality or serious injury in which aircraft were substantially damaged. In the 568 such mishaps studied by the Board, 95.7 percent of the accident aircraft occupants lived. There were survivors in all but a handful of the 71 accidents that resulted in at least one fatality. The survival percentage would have been even higher had it not been for the 1996 losses of a burning ValuJet DC-9 in Florida and TWA 800, a 747 that exploded a few minutes after takeoff from New York JFK Airport. All 340 people aboard both those aircraft were killed.

The Government Accountability Office (GAO, known until July 31 as the General Accounting Office), the investigative arm of Congress, believes that survivable accidents can be made even more survivable. The NTSB, FAA and Amsafe all seem to agree. Phoenix-based Amsafe, currently the only supplier of certified inflatable seatbelt restraints for fixed-wing aircraft occupants, believes these airbag-based systems have the potential to save a significant number of people who would otherwise die from post-crash injuries.

The FAA examined a set of survivable accidents that had occurred in the U.S. between 1970 and 1995 and found that 68 percent of occupants who died in aircraft accidents did so as a direct result of post-crash fire.

Proven on the Highway

The value of airbags on the ground is beyond doubt. The National Highway Traffic Safety Administration reported in January last year that “airbags have saved 10,271 lives,” and the Insurance Institute for Highway Safety states that airbag restraints are “81 percent effective for head injuries.”

Regarding aviation, a GAO report to the House Committee on Transportation and Infrastructure lists 28 technical advancements with potential to further improve aircraft cabin safety and health. Fourteen are “mature, currently available” systems, and Amsafe’s inflatable lap seatbelts are among the most prominently mentioned. Although the report did not mention Amsafe by name, referring to it only as “the manufacturer,” it stated that Amsafe’s product is likely to reduce instances in which “a passenger loses consciousness because of a head injury.” It added that “even a minor nonfatal concussion can cause death if the airplane is burning and the passenger cannot evacuate.”

Amsafe supplies 90 percent of the standard two-point passenger restraint lap belts aboard airliners today, as well as a large share of passenger restraints for general aviation aircraft. The Amsafe Aviation Inflatable Restraint (AAIR) lap-belt airbag system, which has been flying with nine regional airlines and eight majors as of July, uses exactly the same seatbelt hardware and attach points.

The latest inflating lap-belt version, already on 2,683 seats on 140 aircraft, adds only two pounds of net weight per seat with the airbag, inflation tank and sensor/actuator electronics unit. One of these electronics module assemblies (EMA) will sense crash-level longitudinal acceleration and trigger airbag inflation for up to three seats.

The AAIR is battery activated and wholly independent of aircraft power. It is now flying aboard Airbus A319s, A320s, A321s, A330-200s, A340-500s and A340-600s; Boeing 747s and 777s; and Bombardier CRJ700s.

Now Amsafe is penetrating the general aviation market with its AAIR. The first platforms for inflatable lap-belt restraint are piston singles, including the Mooney Bravo and Ovation, Aviat Husky and Zenair models, as well as the new Australian Gippsland GA-8 AirVan utility airplane. All involve straightforward mounting and operation to keep rear passengers’ faces off the front seat backs and the pilot’s head off the control yoke and instrument panel in the event of a crash.

Larry Williams, Amsafe’s director of sales and marketing, said in early July that he has “another major announcement pending” later this year and hinted that it may be a high-volume general aviation OEM order. He said Amsafe is testing inflatable seatbelt systems designed specifically for cabin-class aircraft, especially business jets.
There are peculiar technical problems and challenges with executive aircraft, such as airbag control and “support technologies” due to the wide range of seat orientation and placement patterns among corporate interiors, he explained. The recent certification aboard a transport-category aircraft of seats offset 40 degrees from the airplane’s longitudinal axis has eased some of those challenges.

Williams said a combined seat and inflatable seatbelt “will have to be certified as a system” for each specific aircraft type and cabin configuration within a type. Thus it will be more cost effective, at least initially, for Amsafe to work through airframe OEMs to make AAIR part of a type certificate rather than attempting individual installations through completion or mod centers.

In a Camry, Why Not a G500?

He predicted that as airline use of the AAIR increases, economy of scale will work to reduce unit costs and make the system more attractive in the corporate/executive market. The GAO report to Congress notes that, based on Amsafe projections, “If 5 percent of all U.S. seat positions were equipped with the devices…the cost would drop to about $300 to $600 per seat, including installations.” Williams said he expects corporate pilots and executives alike soon to begin asking themselves, “Why can’t I have the same level of protection in my $20 million aircraft as I have in my $20,000 car?”

The Amsafe executive, who was an aircraft accident investigator before joining the company, said, “The insurance industry has been very favorable toward the inflatable aviation restraint, based on its automotive experience, but rates won’t start reflecting that right away. It will respond only to a demonstrated loss history” (actual “saves” attributable to inflatable restraints).

Amsafe has done its own “assessed benefit” analysis of how many lives might have been saved and injuries averted or lessened had inflatable lap-belt restraints been installed on eight airliners that crashed, causing anywhere from two to 134 fatalities each, between August 1985 and April 1993. Of the 602 total fatalities, Amsafe estimates, 50 could have been avoided had the AAIR system been installed. Further, 65 of the 334 seriously injured might have been hurt less badly or not at all if AAIR systems had been in place to avoid or minimize incapacitating head injuries, the company believes.

Its conclusions are similar to those in the GAO report and the NTSB safety report, Survivability of Accidents Involving Part 121 U.S. Air Carrier Operations, 1983 through 2000, issued in March 2001.

Apples and Oranges

Although based on the same principle as automotive airbags, Amsafe’s aerial version bears little resemblance to its ground-bound counterpart. Whereas the auto airbag is structure-mounted and inflates toward occupants, the AAIR is attached to the lap belt and expands upward and away from the wearer’s torso. Instead of the hot gas generated by a chemical reaction in the automotive product, the aviation restraint bag is inflated from a small tube of compressed helium, an inert gas that cools as it expands. And while the auto airbag inflates and deflates rapidly, the AAIR bag becomes a softer support under lower pressure, then collapses during a 10-second interval.

The AAIR is designed to protect against cranial injury by limiting both the distance an occupant’s head travels and the speed at which it moves during a crash deceleration event, consistent with the FAA’s 16g acceleration resistance criterion for seats themselves. In contrast, an auto airbag is designed momentarily to immobilize an occupant’s entire body.