Sunday, April 1, 2007
Aftermarket: The Seat's the Thing
THEY ARE MORE THAN PIECES OF TAUT MATERIAL stretched across rods in an aircraft. Today, the seats in a helicopter can be quite plush and comfortable, making the ride an enjoyable experience even in the bumpiest of weather. Whereas once, safety might have meant a snugly fastened seat belt (if that), the modern-day rotorcraft seat has all the elements of a highly regulated, highly tested piece of machinery that, in an emergency situation, may mean the difference between being able to walk away from a hard landing or not walking away at all.
Seats are designed for the worst-case scenario. If the crash is particularly hard, people can suffer broken backs and severed spines, which can make it nearly impossible to get out of the helicopter. If an occupant is not wearing a harness, he can impale himself on the cyclic or slam his head on the glareshield or seat in front of him. Depending on the vertical load, the impact may pull the body’s organs down.
It is the FAA that, through research and development as well as extensive testing, sets the requirements for a seat. To set the regulations, a team of experts from industry and certification authorities develop the appropriate standards.
Dave Downey, manager of the FAA’s Rotorcraft Division, said helicopter manufacturers may design their own seat in accordance with FAA regulations. Or the helicopter company may purchase a seat that meets the design criteria. Downey has been with the FAA for 12 years.
Parts 27 and 29 of the Federal Aviation Regulations specify the requirements for certification of seats installed in rotorcraft. The manufacturer of a seat may request a type certificate to certify that it meets all applicable FAA certification standards or a supplemental type certificate to signify FAA approval of its design and installation. The FAA may also issue a technical standard order (TSO) for seat design. A TSO is a minimum performance standard for specified materials, parts, and appliances used in civilian aircraft. Receiving a TSO authorization means the part is approved for both design and production.
FAR 27.785 states "each seat, safety belt, harness and adjacent part of the rotorcraft" designed for use during takeoff and landing must have no potentially injurious objects, sharp edges, protuberances, or hard surfaces. Also they must be designed so that someone properly using them will not be injured seriously in an emergency landing by specific static inertial load factors and dynamic conditions. Those loads and conditions are specified in 27.561(b) and 27.562, respectively.
Approval of seats is a step-by-step process that may be modified depending on the requested seat certification. The first step is to apply for certification through the appropriate Aircraft Certification Office. These offices are located throughout the country.
Someone proposing a new seat or seat installation must submit a certification plan outlining the applicable regulatory requirements and the proposed method of compliance with them. These proposals typically include testing and analysis.
The FAA must agree that the plan complies with the regulations.
The applicant must then submit the data needed for certification, including design drawings, analyses, test plans and results, and other necessary data.
If all is in order, the FAA grants approval of the design. At that point, the seat may be installed in a specified rotorcraft. Installation approval must also be granted.
Once the requirements are met, the helicopter manufacturer seeks out a seat that fits its design and the requirements of the buyer.
Armor Holdings, a Jacksonville, Fla.-based firm with interests in aviation and defense, has designed FAA-approved rotorcraft and fixed-wing seats for more than 30 years. It designed the seats for the U.S. Marine Corps VH-71, the new presidential helicopter being developed by Lockheed Martin, AgustaWestland, and Bell Helicopter.
Brian Willet, director of programs and sales for Armor Holdings, said that during the Vietnam War the helicopter accident fatality rate was high and many soldiers suffered broken backs and necks because their seats were not designed to take the impact of a hard landing.
Armor has incorporated "energy absorbers" into the seat design in which the seat slides down a guide tube and absorbs the energy of the crash. The impact is "not imparted to the passenger," said Willet.
Willet noted guidelines for the military can be different than for civilian rotorcraft.
Seats in civilian helicopters must be designed to meet a lumbar load of no more than 1,500 lb. Seats designed for military helicopters must be able to absorb a lumbar load of 2,500 lb. It is assumed, said Joe Shane, vice president for business development at Armor, the person in a military seat is generally younger and carrying heavy equipment.
Fischer+Entwicklungen GmbH (F+E) manufactures seats in Landshut, Germany. In addition to producing seats for helicopters for certification, it has its own test facility. "We are able to design, test and get the documents to give to the customer," said Jeff Hall, the company’s representative in the U.S. F+E has designed seats for Eurocopter, AgustaWestland, and Sikorsky. "The challenge is to stay within the weight limitation," he said, explaining they try to make the seat as light as possible but still crashworthy.
"We are driven by the FAR crashworthiness," he said, noting the different certification agencies from Europe, Asia, and the U.S. work together.
In addition, there are different requirements for seats depending on the aircraft’s purpose. For example, if the helicopter will be used to give tours, the seats must conform to FAR Part 135, said Tony Erickson, a research and development engineer with Oregon Aero in Scappoose, Ore. Different FAA regulations relate to different aircraft missions.
Seats must also meet a "burn" regulation. Proposed seats are taken to a burn lab and tested to see if they "burn out, or self-extinguish themselves," said Erickson.
Claire Gordon is a senior research scientist with the U.S. Army’s Soldier Systems Center in Natick, Mass. She also is an adjunct professor at Arizona State University and has been instrumental in designing all manner of equipment for soldiers based on her expertise in anthropometry, the study of human body measurement.
Her research, measuring more than 132 body dimensions, enables seat designers to propose seat dimensions. A study involving 10,000 soldiers, male and female conducted in 1988, measured not just height and weight, but other body dimensions including, for example, the distance from the shoulder to the end of the fingers and from the tip of one’s toes to the top of the leg.
To ensure the crashworthiness of a seat, said Gordon, the weight of the soldier must be taken into account and the seat designed for the worst-case scenario.
A seat is designed to accommodate all but the five percent tallest and heaviest men and the five percent smallest and lightest women. The concept is much like that of a bell curve, where the majority of the subjects fall within the boundaries of the curve.
The seat must be as safe and comfortable for a small female as it would be for a large male.
To answer this concern, Armor designed an "inversion tube" installed in the seat that allows the seat to stroke down at a controlled rate. "All the shock goes into the seat instead of the spine," said Willet.
Armor has also designed a seat with a variable load energy absorber, a dial on the side of the seat that allows the occupant to put in his or her weight. The seat is designed to compensate for the weight and absorbs the impact of a possible hard landing.
With technology, g forces have increased, said Frank Robinson, president and CEO of Robinson Helicopters, making it necessary to conduct dynamic tests, with the aircraft moving. These tests are designed to ensure the seat functions as it was designed. A seat can go through several iterations before it is offered to the FAA for its approval.
And, according to Erickson, it can take more than two years to get a seat approved by the FAA.
Being certified for one aircraft does not automatically mean the seat is certified for any other aircraft. Each time a new aircraft is designed, the seat, even if the FAA has already certified it, must go through the certification process again.