Schroth Safety Products LLC’s senior vice president (Aerospace) Sean Padfield discusses the certification of airline seatbelts
[This article first appeared in the November/ December 2021 issue of Airline Cabin Management]
When you sit down in an aeroplane and buckle your seatbelt, have you ever thought about what that restraint goes through in order to be certified as airworthy? For those not in the aircraft seating industry, it can be surprisingly complex to integrate passenger restraint systems into aircraft seating.
The Wright Brothers first installed a seatbelt in their aeroplanes in 1910 but it would be many years until they were made mandatory.
Speaking at the 1929 aeronautical meeting of the American Society of Mechanical Engineers, Charles N Monteith, chief engineer at Boeing Airplane Company, emphasised the need for passenger seatbelts. “British and Dutch opinion is against their installation,” he told the delegates, “and most of the transports operating in the United States today do not provide belts for the passengers. However, it is being demonstrated rapidly that they are sometimes very necessary.”
Monteith went on to explain that safety belts not only protected passengers in the event of a crash, they also reduced the risk of injuries in turbulent air. However, it would not be until 1972 that aviation requirements for basic safety features, including passenger safety belts, were solidified.
Today, regulations from civil aviation authorities like the US FAA and Europe’s EASA are just the starting point. The primary legislation is contained in the sections of the FAA’s 14 CFR Part 25 or EASA’s CS‑25. Section 25.785 specifically covers safety belts.
Certain aircraft equipment is certified against the FAA Technical Standard Order (TSO) or EASA European Technical Standard Order (ETSO), and for seatbelts and restraint systems that is TSO- or ETSO‑C22(g) and C114. These TSO/ETSO documents refer onwards to minimum performance standards set by SAE International.
It is when a novel or innovative seat, or other product, isn’t covered in the TSO/ETSO documents that things get complicated with individual certification demonstration processes often required. The FAA designates these as Special Conditions, and EASA refers to them as Certification Review Items, but they are both formal methods of certifying cutting‑edge technologies.
Head Injury Criterion
At the end of the day, the seatbelt is there to protect a passenger during a crash, which itself is a massively complex scenario, driving a wide range of requirements. For example, testing requirements include static trials of seats independently, seats in rows with others, interaction with monuments in front of seats — and that’s before other important requirements like flammability, smoke toxicity and resistance to chemical corrosion enter the equation.
One of the more complicated elements of the seat belt certification process is the Head Injury Criterion (HIC). HIC is a measure of the likelihood of a head injury arising from an impact: in this case, the forward and rebound motion in a typical crash scenario. It considers the magnitude of head acceleration as well as the duration of the acceleration. At Schroth Safety Products, this calculated value is predicted through Computational Fluid Dynamics (CFD) analysis and verified through testing. The design of seatbelt products takes into account the overall head arch of the passenger and the HIC to select the best solution for the specific aircraft seat.
In economy class, seats in most rows use a breakover feature which allows the seatback to pivot during an impact — to act as a crumple zone. Standard two-point lap belts, what most people would think of as the usual airline seatbelt, is typically sufficient for these standard configurations.
In exit rows, seats must remain in place so as not to impede evacuation, requiring the passenger behind to be spaced far enough back for the passenger’s head to miss the exit row seat during a crash event. In bulkhead (typically first row economy) seats, too, either the passenger must be spaced far enough behind to completely miss the bulkhead, or a restraint system or airbag must be used. In most airline cases, the airbag is contained within a lap belt.
Meanwhile, in premium economy, business and first class cabins it’s even more complicated, with seats angled away from the centreline of the aircraft, seats facing towards the side or rear, feature elements or privacy wings, suite doors and much more that can come into play. These require more complex solutions such as three-point pretensioner restraints and structure mounted airbags.
At Schroth Safety Products we have compiled a white paper looking at aircraft seat belts and helping customers to navigate the complex web of regulations, testing and updates. If you would like a copy, please get in contact.
With the cabin interior evolving at a faster rate than ever before, innovation in the safety belt market is more critical than ever.