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61 3 Crashworthiness and Other Safety Considerations With the exception of regulations governing school bus passenger trans- portation and crash protection,1 the federal government has not estab- lished safety standards that apply to wheelchair securement systems or wheelchairs used as seats in surface transportation vehicles or airplanes.2 Nevertheless, wheelchairs and securement systems that are designed and constructed according to voluntary industry standards intended to ensure safer transportation for people who must use their personal wheelchairs as seats in motor vehicles are currently in use. As explained in Chapter 2, the standards are issued by the Rehabilitation Engineering and As- sistive Technology Society of North America (RESNA), a not-for-profit professional association dedicated to promoting the health and well-being of people with disabilities through access to technology. The RESNA standards cover design requirements, performance criteria, test meth- ods, and product labeling for wheelchair tiedown and occupant restraint 1 An exception are regulations governing school bus passenger transportation and crash protection (Federal Motor Vehicle Safety Standards [FMVSS] 222). 2 Title 14 CFR Part 382, administered by the U.S. Department of Transportation, does con- tain requirements for manual wheelchair cabin stowage and the provision of aisle wheelchairs, but these are not safety-related standards and do not pertain to the securement and use of wheelchairs when used as seats in airplanes.
62 WHEELCHAIR SECUREMENT CONCEPT FOR AIRLINE TRAVEL systems (WTORS) and for wheelchairs that may be used as seats in motor vehicles.3 Although it was created in 1979 and has been issuing wheelchair trans- portation safety standards since the 1990s, RESNA has not established standards for the safe securement and use of wheelchairs in passenger airplanes. All U.S. safety regulations governing aircraft design certification are administered by the Federal Aviation Administration (FAA). The main body of FAA regulations that applies to the cabin interiors of airplanes is in Title 14 Part 25 of the Code of Federal Regulations (14 CFR 25). These regulations are intended to ensure cabin interior âcrashworthiness,â a term used by FAA in reference to a âsurvivable crashâ when the cabin occupants are subjected to crash forces within human tolerances and the structural integrity of the passenger space remains intact such that the occupants can rapidly evacuate.4 While the Part 25 regulations do not refer to WTORS or wheelchairs used as passenger seats, they govern most aspects of the performance, design, and testing of airplane seats, including their occu- pant restraint systems and supporting structures and attachment to the floor and primary airplane structure. Of particular relevance to seats are the Part 25 sections intended to protect airplane occupants during crash conditions in an emergency landing, prevent items of mass from shifting or becoming loose and creating a hazard to occupants, and minimize the potential for and severity of a post-crash fire. A review of these applicable Part 25 requirements is therefore important inasmuch as FAA may require satisfactory demonstration that secured wheelchairs can meet the same crashworthiness performance criteria as airplane seats. The remainder of the chapter begins with a review of the relevant FAA Part 25 requirements and the RESNA standards for WTORS and wheelchairs when used as seats for motor vehicle transportation. The FAA and RESNA requirements are then compared, with an emphasis on both alignments be- tween the two and differences and gaps, particularly with respect to whether and how compliance with RESNA standards could satisfy the crashworthi- ness criteria of the Part 25 requirements. The findings from these compari- sons inform the assessment of the space within an airplane cabin that would 3 RESNAâs Assistive Technology Standards are approved for publication as American National Standards by the American National Standards Institute (ANSI), ensuring that the standards development process meets ANSIâs essential requirements for openness, balance, consensus, and due process. The standards are grouped under the general title ANSI/RESNA WC-4. See ANSI/RESNA. 2017. âWC-4:2017 American National Standard for Wheelchairsâ Volume 4: Wheelchairs and Transportation.â https://www.resna.org/Portals/0/Documents/ AT_WC4_SellSheet_8.13.19.pdf. 4 FAA. 2009. Advisory Circular 25-17AââTransport Airplane Cabin Interiors Crashwor- thiness Handbook. https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/ document.information/documentid/74596.
CRASHWORTHINESS AND OTHER SAFETY CONSIDERATIONS 63 be needed for a wheelchair to be positioned and secured in Chapter 4 and the summary assessment of the technical issues, challenges, and uncertainties associated with a wheelchair securement system concept in Chapter 5. FAA CABIN INTERIOR CRASHWORTHINESS REQUIREMENTS FAAâs aviation safety regulations in 14 CFR are organized into more than 40 parts, each addressing a specific activity, such as the flight rules govern- ing aircraft operation and the certification of pilots, aircraft, and aircraft technicians. Part 25 is titled âAirworthiness Standards: Transport Category Airplanes.â Transport category airplanes are defined as jet airplanes with 10 or more seats and turboprop and other propeller-driven airplanes with 20 or more seats, which essentially covers all passenger airplanes in scheduled service. Historically, the emphasis of federal safety regulations was on en- suring aircraft airworthiness;5 however, by the 1960s additional emphasis was placed on ensuring crashworthiness as technical knowledge was gained from research and service experience and as crash investigations permitted the development of interior design parameters to aid in crash survival.6 The major regulatory sections of Part 25 that pertain to crashworthiness requirements for cabin interiors are shown in Box 3-1. FAAâs approach to cabin crashworthiness has principally involved three areas of concern: (1) protecting cabin occupants from crash impact, (2) minimizing the potential for and severity of a post-crash fire in the cabin, and (3) rapidly evacuating the cabin in the event of an emergency. Some of the Part 25 sections intended for these purposes pertain directly to the design and configuration of passenger seats and are thus most pertinent to a review of the technical issues associated with in-cabin securement of wheel- chairs and their use as seats in an airplane. Of particular interest are the requirements governing the performance of cabin interior components dur- ing emergency landing conditions (Â§ 25.561 and Â§ 25.562), seats and safety belts (Â§ 25.785), retention of items of mass (Â§ 25.789), and flammability of seat cushions and coverings (Â§ 25.853). An important point regarding these four sets of requirements, which are described next, is that each is intended to serve two purposes: (1) to protect the seatâs occupant by reducing the potential for serious or fatal injuries and (2) to protect occupants of the airplane generally by reducing the potential for fires, obstructions to rapid evacuation, and loose objects becoming hazards. 5 According to 14 CFR Part 25 Â§ 3.5(a) airworthy means an aircraft conforms to its type design and is in a condition for safe operation. 6 FAA. 2009. Advisory Circular 25-17AââTransport Airplane Cabin Interiors Crashworthi- ness Handbook, p. ii. https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/ go/document.information/documentid/74596.
64 WHEELCHAIR SECUREMENT CONCEPT FOR AIRLINE TRAVEL BOX 3-1 Crashworthiness Requirements for Cabin Inferiors of Transport Category Airplanes: Major Sections. Title 14 Part 25 of the Code of Federal Regulations (14 CFR 25) Section 25.561 Emergency Landing Conditions General Section 25.562 Emergency Landing Dynamic Conditions Section 25.772 Pilot Compartment Doors Section 25.783 Doors Section 25.785 Seats, Berths, Safety Belts, and Harnesses Section 25.787 Stowage Compartments Section 25.789 Retention of Items of Mass Section 25.791 Passenger Information Signs Section 25.793 Floor Surfaces Section 25.795 Security Considerations Section 25.801 Ditching Section 25.803 Emergency Evacuation Section 25.805 Flight Crew Emergency Exits Section 25.807 Passenger Emergency Exits Section 25.809 Emergency Exit Arrangement Section 25.810 Emergency Egress Assist Means and Escape Routes Section 25.811 Emergency Exit Marking Section 25.812 Emergency Lighting Section 25.813 Emergency Exit Access Section 25.815 Width of Main Aisle Section 25.817 Maximum Number of Seats Abreast Section 25.819 Lower Deck Service Compartments (Including Galleys) Section 25.851 Fire Extinguishers Section 25.853 Compartment Interiors Section 25.854 Lavatory Fire Protection Section 25.855 Cargo and Baggage Compartments Section 25.856 Thermal/Acoustic Insulation Materials Section 25.857 Cargo Compartment Classification Section 25.869 Fire Protection: Systems Section 25.1307 Miscellaneous Equipment Section 25.1359 Electrical System Fire and Smoke Protection Section 25.1411 Safety Equipment â General Section 25.1413 Safety Belts Section 25.1415 Ditching Equipment Section 25.1421 Megaphones Section 25.1423 Public Address Systems Section 25.1439 (a) Protective Breathing Equipment Section 25.1447 Equipment Standards for Oxygen Dispensing Units Section 25.1451 Fire Protection for Oxygen Equipment Section 25.1541 Markings and Placards â General Section 25.1557 (a), (c), and (d) Miscellaneous Markings and Placards Section 25.1561 Safety Equipment
CRASHWORTHINESS AND OTHER SAFETY CONSIDERATIONS 65 Note that several of the other Part 25 requirements for cabin crash- worthiness that are listed in Box 3-1 do not pertain directly to passenger seats, but the airplaneâs seating can nevertheless play an important role in enabling compliance. For instance, Part 25 contains performance require- ments for an emergency evacuation (Â§ 25.803), which must be possible within 90 seconds, and therefore seats are generally designed and config- ured to help achieve this performance mandate.7 In addition, Part 25 con- tains other cabin safety requirements that are often satisfied with the help of cabin seats, such as by housing flotation devices (Â§ 25.1415) and by provid- ing handgrips (as part of Â§ 25.785) and emergency lighting (Â§ 25.1415). In all of these cases, however, the regulations do not mandate a specific role for seats, and the performance-based nature of FAA requirements means that airplane manufacturers and interior designers have latitude for decid- ing how they will meet them. Because of this opportunity for innovation by interior designers, it is not possible to know exactly how they would try to satisfy FAA performance-based requirements where a wheelchair is used as a seat. However, in having this latitude, it is also reasonable to assume that designers would indeed be able to come up with solutions through the ap- plication of creative design and engineering approaches. Accordingly, these and other similar Part 25 requirements that can reasonably be met through an ordinary level of design and engineering creativity and effort are not considered further in this chapter, which focuses on identifying potentially significant technical challenges. Emergency Landing Conditions (Â§ 25.561 and Â§ 25.562) When the Part 25 crashworthiness requirements were introduced, they con- tained a single section (Â§ 25.561) on emergency landing conditions, which stipulated certain resting, or static, load forces that the airplane, including seating systems and their supporting structure and items of mass, must be able to withstand without deforming to a degree that would impede rapid evacuation of the airplane. The forces were given as static strength require- ments for different loading directions and expressed in multiples of the acceleration of gravity, or g. The static load factors, as stipulated today, are (1) upward 3 g, (2) forward 9 g, (3) sideward 3 g (airframe) and 4 g (seats), (4) downward 6 g, and (5) rearward 1.5 g. The static load testing procedure is typically accomplished by applying a force to the seat through the safety belt by means of a hydraulic or cable and winch system. For instance, in testing the forward direction, the minimum force that the seat 7 Currently, passengers who are nonambulatory and seated in airplane seats will need as- sistance in the event of an evacuation, and that same assistance would presumably be needed by nonambulatory passengers seated in wheelchairs.
66 WHEELCHAIR SECUREMENT CONCEPT FOR AIRLINE TRAVEL must be capable of withstanding without structural failure is nine times the combined weight of the seat and a 170-lb occupant. In 1988, a new section, Â§ 25.562, was added that includes dynamic force performance standards for seating systems intended to provide in- creased occupant protection in survivable crashes. Two separate dynamic tests are conducted to simulate two different crash scenarios. In the first test, the impact vector is predominantly vertical (in combination with a forward force component) from an airplane descending to impact, such as during an emergency landing with a high descent rate. The vertical test demonstrates the seat structureâs ability to avoid severe deformation, retain items of mass, and protect the occupant from spinal injury under vertical loadings. In the second test, the impact vector is predominantly horizontal from an airplane moving forward and slightly sideways to impact, such as on the runway or ground where the main impact force is along the air- planeâs longitudinal axis but with a lateral impact component, as might oc- cur during a hard landing. The test procedures require rapidly decelerating the seat. In the vertical test, each seat must be able to withstand a change in downward vertical velocity from 35 to 0 ft per second (i.e., from 24 to 0 mph) in not more than 0.08 seconds, with the airplaneâs longitudinal axis canted downward 30 degrees with respect to the horizontal plane and with the wings level. A peak floor deceleration of at least 14 g must occur after impact. In the longitudinal test, deceleration must go from 44 to 0 ft per second (30 to 0 mph) in not more than 0.09 seconds and with the airplaneâs longitudinal axis horizontal and yawed 10 degrees either right or left with the wings level. A peak floor deceleration of at least 16 g must occur after impact.8 Passenger seats are also tested with a 170-lb anthropomorphic test dummy (ATD), or its equivalent, sitting in the normal upright position and instrumented to measure forces and accelerations.9 The testing requires that the lap belt remain on the ATDâs pelvis during the impact. Protection from impact forces must be provided in situations where the testing indicates that the occupantâs head could strike seats or other surfaces such that a 8 Because Â§ 25.562 did not take effect in new aircraft until the mid-1990s and was applied to only newly type certificated aircraft, seat strength requirements can vary among airplanes in the existing fleet depending on the type of aircraft and when that aircraft model was first certi- fied. A Boeing 767-300, for instance, only requires passenger seating to meet static strength requirements, whereas a newer Boeing 787 requires testing for both static and dynamic load- ing. However, with the passage of Â§ 121.311(j) all transport passenger aircraft manufactured on or after October 27, 2009, must meet the requirements of Â§ 25.562. This requirement has led to very few 9 g seats being installed on aircraft where their installation is still permitted. 9 49 CFR Part 572, Subpart B.
CRASHWORTHINESS AND OTHER SAFETY CONSIDERATIONS 67 head injury criterion (HIC) of 1,000 units is not exceeded.10 The maximum compressive load measured between the pelvis and the lumbar column of the ATD must not exceed 1,500 lb, as protection against a spinal column injury, and axial compressive loads on the femur must not exceed 2,250 lb, as protection against a debilitating leg injury such as through knee contact with seats or other structures in front of the passenger.11 Photos depicting sequences during both types of dynamic tests are shown in Figure 3-1.12 The dynamic testing process is significantly more complicated than the static testing process because the head and leg injury criteria can only be completely evaluated when the seat is considered in relationship to where it is installed in the airplane.13 For example, the testing will cause the upper torso and head to swing forward in an arcing motion because the ATD is constrained only at the pelvis by the safety belt. A record of the motion of the head through the arc is used during the installation approval process to ensure there is enough clearance from hard surfaces and objects, such as unpadded bulkheads, to reduce the possibility of injurious head impact. The striking radius of the head is considered to be an arc of 35 in. from the cushion reference point, the point where the back cushion and bottom cushion intersect at the center of the passenger seat.14 If all seats were uniformly installed at the same distance from one row to the next in every airplane, only a few head-path reviews would be re- quired. However, this is not the case because cabin configurations vary from one airplane to the next and from one airline to the next. Some airlines will have different seat configurations within the same airplane model in their fleets. Because cabin interior arrangements differ, the head-path must be evaluated for each unique installation. 10 HIC is a quantitative measure of head injury risk in crash situations. The HIC 1,000 value was consistent with acceptable head injury protection levels for a mid-size adult when an airbag is activated in a motor vehicle crash, as defined in FMVSS at the time FAA adopted the dynamic testing requirements for airplane seats. 11 The leg injury criteria also have their origins in FMVSS. 12 The weight of the ATDs used in motor vehicle testing, wheelchair testing, and airplane seat testing is less than the average weight of an adult age 20 or over in the United States. See Centers for Disease Control and Prevention National Center for Health Statistics. 2021. âBody Measurements.â https://www.cdc.gov/nchs/fastats/body-measurements.htm. 13 The discussion of the dynamic testing process that follows derives from the original text and descriptions in FAA. 2005. âImproved Seats in Air Carrier Transport Category Airplanes: Final Rule.â Federal Register 70, no. 186: 56541â56559. 14 More specifically, the striking radius of the head is considered to be an arc of 35 in. whose center is at the intersection of the plane of the uncompressed top of the seat cushion with the plane of the uncompressed front of the back cushion; this is commonly referred to as the cushion reference point.
68 WHEELCHAIR SECUREMENT CONCEPT FOR AIRLINE TRAVEL Seating systems are also dynamically tested with regard to the integrity and strength of their attachment to the seat tracks and floor beams. When they are being tested in the longitudinal direction, seat tracks and seat at- tachments that hold the seats to the test fixture must be misaligned with respect to the adjacent set of tracks by at least 10 degrees vertically with one rolled 10 degrees. During the testing, the seats must remain attached at all points and not yield to an extent that they could impede rapid evacu- ation of the airplane. Additional requirements pertaining to seating system attachments are prescribed in the section on Seats, Berths, Safety Belts, and Harnesses (Â§ 25.785), as noted below. For reference, a drawing of a typi- cal economy class seat assembly and attachments to seat tracks is shown in Figure 3-2a. An illustration of floor and seat deformation is provided in Figure 3-2b. Seats, Berths, Safety Belts, and Harnesses (Â§ 25.785) Â§ 25.785 stipulates that each airplane seating system, including the occu- pant restraint system, must be designed so that an occupant making proper use of it will not sustain serious injury in an emergency landing as a result of the static and dynamic forces specified in Â§ 25.561 and Â§ 25.562. The FIGURE 3-1 Dynamic tests (vertical [14 g] and longitudinal [16 g]) to demonstrate compliance with Â§ 25.562. NOTES: The images are from a sled running on a horizontal track, which is the typical test facility. Accordingly, for the vertical test setup using a horizontal track, the seat is rotated backward 60 degrees to meet the regulatory criteria for this test condition (i.e., canted downward 30 degrees). The images show the ATDs at near peak movement. In the vertical test, the typical sequence is that the ATD initially slumps down in the seat, which compresses the spine to create the maximum lumbar load. In the longitudinal test, the typical sequence is that the ATD slides forward until the lap belt reaches maximum stretch, at which point the upper torso and head rotate forward and legs flail.
CRASHWORTHINESS AND OTHER SAFETY CONSIDERATIONS 69 section further states that each occupant of a seat must be protected from head injury by a safety belt (equipped with a metal-to-metal latch) and, as appropriate to the seatâs type, location, and facing angle, by one or more of the following: (1) a shoulder harness that will prevent the head from contacting any injurious object; (2) the elimination of any injurious object within striking radius of the head; and (3) energy absorbing rest that will support the arms, shoulders, head, and spine. Furthermore, any projecting objects that could injure people seated or moving about the airplane in normal flight must be padded. Â§ 25.785 states that each seat, supporting structure, belt, and belt anchorage must be designed for an occupant weighing 170 lb. The regula- tion requires that the seating system be designed to withstand all flight and ground load conditions, including those specified in Â§ 25.561 and Â§ 25.562. The static forces specified in Â§ 25.561 must be multiplied by a factor of 1.33 in determining the strength of the attachment fittings of each seat to the structure and each belt to the seat and structure. Retention of Items of Mass in the Passenger Compartment (Â§ 25.789) Â§ 25.789 prescribes that each item of mass in the passenger compartment that is part of the airplane type design, including parts of seating systems, be prevented from becoming a hazard by shifting or becoming a projectile in the cabin due to application of the maximum loading conditions cor- responding to the specified flight and ground load conditions and to emer- gency landing conditions specified in Â§ 25.561. Compliance is demonstrated through the static testing conducted for Â§ 25.561. Although retention of FIGURE 3-2 Illustrations of (a) a typical economy class passenger seat assembly and attachment to seat track, and (b) the floor and seat deformation position. SOURCE: (b) SAE International. (a) (b)
70 WHEELCHAIR SECUREMENT CONCEPT FOR AIRLINE TRAVEL items of mass is not explicitly mentioned in the Â§ 25.562 requirement for dynamic testing, it is typically demonstrated for seating systems during these tests. Compartment Interiors Flammability (Â§ 25.853) Â§ 25.853 prescribes that all materials in the passenger cabin successfully complete flammability performance criteria to demonstrate that they are self-extinguishing. The test must be performed using a small-flame Bunsen burner. The seat cushions, seat covers, and all other materials used in the seating system, including finishes or decorative surfaces applied to the materials, must meet the criteria. In addition, all seat cushions and covers must successfully complete flammability testing that prescribes use of a large-flame oil burner to ensure that a fire will not propagate throughout the cabin due to cushions burning. WHEELCHAIR TRANSPORTATION SAFETY STANDARDS There are two common approaches used for providing adequate safety and crash protection of passengers who remain seated in wheelchairs while riding in motor vehicles: (1) securement and (2) containment. Securement involves connecting the wheelchair frame to the vehicle by using some form of attachment points. Containment involves creating a defined space for the occupant and the wheelchair that is separate from the space of other pas- sengers, such as by employing a barrier to prevent ingress of the wheelchair into the space of other passengers. For vehicles subject to high levels of acceleration, such as passenger cars and light buses, the emphasis is usu- ally placed on good securement. For large, slower-moving vehicles, such as public transit buses, ensuring effective containment is usually emphasized. The former crash environment is frequently referred to as âhigh gâ and the latter environment as âlow g.â When a person remains in the wheelchair during transportation in a passenger car or light bus (i.e., high-g environment), the wheelchair must take on the role of a vehicle seat according to the securement approach. Just as a conventional seat is rigidly anchored to the vehicle chassis, the wheelchair must be secured in the vehicle so that it does not move sub- stantially during a crash or emergency maneuver.15 When anchored, the wheelchair should not become a projectile that endangers vehicle occupants in a collision. Securement should reduce the chance that the wheelchair mass loads the occupant, adding to a seat beltâs ability to limit occupant movement within the vehicle. The wheelchair should support the occupant 15 In the frontal impact test, there is a 200-mm horizontal excursion limit.
CRASHWORTHINESS AND OTHER SAFETY CONSIDERATIONS 71 throughout the crash event so that a properly positioned seat belt engages with the strong parts of the occupantâs skeletal structure. Accordingly, the seat design should not interfere with proper placement of seat belts or cause failure of belt components during dynamic loading. As described in Chapter 2, RESNA standards contain four sections that address aspects of wheelchair user transportation safety: Section 10 (WC10) on wheelchair containment and occupant retention systems for use in large accessible transit vehicles,16 Section 18 (WC18) on WTORS, Sec- tion 19 (WC19) on wheelchairs used as seats in motor vehicles, and Section 20 (WC20) on wheelchair seating systems for use in motor vehicles.17 The focus of the discussion that follows is on WC18 and WC19, which are the main RESNA standards governing the safety of wheelchairs when used in motor vehicle transportation. The goal of WC18 is to promote the design and use of WTORS that provide protection for forward-facing occupants in wheelchairs that is comparable to the protection afforded occupants of conventional vehicle seating. The key performance objective of the standard is to reduce the likelihood of serious and fatal injuries to occupants who are involved in frontal vehicle crashes; however, use of WTORS equipment that complies with WC18 was also expected to result in increased safety and security for occupants seated in wheelchairs during normal travel, emergency vehicle maneuvers, and other types of crashes such as vehicle rollovers and side impacts. WC18 was created on the premise that WTORS manufacturers are not able to control the end use of their products, including the types of wheelchairs they secure and the motor vehicles in which they are installed. Accordingly, WC18 emphasizes WTORS design requirements, test pro- cedures, and performance criteria for crashworthiness when used for all types of wheelchairs (manual and power) and for all types and sizes of motor vehicles. The standard calls for dynamically testing the securement and restraint system based on the assumption of a nominally worst-case frontal crash, creating a change in velocity from 30 to 0 mph with an aver- age deceleration pulse of 20 g. The frontal impact test procedure, which is pictured in Figure 3-3, requires the use of a 185-lb rigid mass surrogate 16 In recognition that the likelihood of a moderate-to-severe crash is low in a large acces- sible urban transit vehicle, the WC10 standard, which applies to wheelchair passenger spaces intended for use by rear-facing, wheelchair-seated occupants, is intended to provide a level of safety during travel for passengers seated in wheelchairs that is equivalent to passengers in transit vehicle seats or who are standing using handholds. 17 Because wheelchair seating systems are often provided as aftermarket products, WC20 establishes design and performance requirements and related test methods to evaluate seating systems relative to their use as seats in motor vehicles independent of their installation on production wheelchair frames.
72 WHEELCHAIR SECUREMENT CONCEPT FOR AIRLINE TRAVEL wheelchair occupied by a mid-size adult male ATD (approximately 170 lb) to dynamically load the wheelchair and WTORS, respectively. Wheelchairs that have been tested for crashworthiness using WC19 test methods must include readily identifiable (by a hook symbol) tiedown strap securement points with specified slot-type geometry located near the four corners of the wheelchair. In a typical tiedown arrangement (illustrated in Chapter 2), steel securement points with slot openings are used as wheel- chair attachment points and the tiedown straps terminate with steel hooks to engage with the securement points. In recognition that transportation safety assurance is a system problem, WC19 establishes the design and performance requirements for wheelchairs that may be secured by a WC18-compliant WTORS and used as a seat during motor vehicle transportation. The standard, which applies to both manual and power wheelchairs, was established under the premise that a seat must be effectively secured so that its mass does not add to crash-generated restraint forces on the occupant and so that seat belts will effectively limit occupant movement within the vehicle during a 30-mph, 20-g frontal impact. It further establishes that the seating system must be designed so that it is not the source of occupant injuries, does not interfere with proper placement of belt restraints on the occupant, does not cause failures of belt restraint components during dynamic loading, and supports the occupant throughout the crash event so that belt restraints remain properly positioned on the bony regions of the body such as the pelvis and shoulder. RESNA requirements for wheelchairs used for transportation are summarized in Box 3-2. FIGURE 3-3 Peak-of-action photos for a 30-mph, 20-g frontal impact test of WTORS (WC18) using a 185-lb rigid surrogate wheelchair and a mid-size male ATD. NOTE: Images show two different restraint configurations: lap/shoulder belt (left) and wheelchair-anchored lap belt (right). SOURCE: University of Michigan Transportation Research Institute.
CRASHWORTHINESS AND OTHER SAFETY CONSIDERATIONS 73 Using the same 30-mph, 20-g frontal impact dynamic force test con- ditions specified in WC18, WC19 requires that a wheelchair perform ef- fectively in a moderate-to-severe frontal crash. The performance criteria are intended to ensure that the structural components of the wheelchair BOX 3-2 RESNA Transportation Requirements for Wheelchairs A wheelchair that complies with the RESNA transportation standard has the fol- lowing features: â¢ Four permanently labeled, easily accessible securement-point brackets with specific geometry that allows for one-hand attachment of one or two tiedown hooks from tiedown-strap assemblies by a driver or care- giver reaching from one side of the wheelchair; â¢ A base frame and seating system that, along with the four securement points, have been successfully crash tested in a 30-mph, 20-g frontal impact when loaded by an appropriate-size crash test dummy with the wheelchair secured facing forward by a surrogate four-point, strap-type tiedown; â¢ Tiedown strapâclear paths between the securement points on the wheelchair and typical anchor points on the vehicle floor, such that tiedown straps will not be in close proximity to sharp edges (on the wheelchair) that could cause failure of webbing material when loaded in a frontal crash; â¢ Anchor points that enable the wheelchair occupant to use a wheel- chair-anchored crashworthy pelvic/lap belt to which the lower end of a vehicle-anchored shoulder belt can be readily connected near the occupantâs hip; â¢ A manufacturer-disclosed rating of poor, acceptable, good, or excellent for the wheelchairâs accommodation of properly using and positioning a vehicle-anchored belt restraint; â¢ A measure of wheelchair lateral stability (determined with a lateral tip test) when secured facing forward by a four-point, strap-type tiedown; â¢ Reduction of sharp points and edges that could damage belt restraints or injure passengers; and â¢ Provision for crashworthy retention of wheelchair batteries and motors, and use of gel-cell or sealed batteries to eliminate the potential for acid spills. While most wheelchairs occupied by passengers are secured using strap-type securement systems, WC18 and WC19 also include design and performance criteria for docking systems. In addition, the standards include the requirements for the Universal Docking Interface Geometry, which is intended toÂ allow wheelchair stations of public vehicles to secure many differentÂ types of wheelchairs in high-severity crashes whileÂ allowing for independent use.
74 WHEELCHAIR SECUREMENT CONCEPT FOR AIRLINE TRAVEL securement points do not fail, the points do not deform in a manner that prevents manual disengagement of the tiedown hook, the wheelchair re- mains in an upright position, and the occupant remains in a seated posture in the wheelchair seat. The dynamic loading reveals the strength of the wheelchair frame, belts, and securement points, as well as retention of wheelchair components, including the battery. Another aim of WC19 is to improve the accessibility and ease of at- taching the end fittings of straps and to remove deterrents to the proper and effective use and positioning of belt restraints. Consequently, WC19 ad- dresses the problem of wheelchair occupants not being restrained properly due to wheelchair interference with the positioning of the WTORS belts or the wheelchair occupant wanting to avoid intrusion into personal space by drivers and caregivers assisting with restraint positioning. WC19âs solution is that wheelchair manufacturers offer the option of a dynamically tested wheelchair-anchored pelvic belt that can be fastened by the occupant or another person such as a caregiver. While WC19-compliant wheelchairs do not necessarily come equipped with the pelvic belt, the belts must be offered as an option to purchasers or consumers, and the wheelchairs are crash tested with the prescribed belt. RESNA has developed a label that can be applied to wheelchairs that comply with WC19, as shown in Figure 3-4.18 In addition to developing standards applicable for wheelchairs when used as seats in motor vehicles, RESNA develops standards for wheelchairs that apply to everyday usage. WC16, for instance, provides the requirements and test methods for the ignition of upholstered parts for wheelchairs and seating systems. This standard, as noted below, can have relevance when 18 WC19 also allows an integrated seat and lap belt, with anchored shoulder strap. FIGURE 3-4 RESNA WC19-compliant label and its application on a power wheelchair. SOURCES: RESNA and the University of Michigan Transportation Research Institute.
CRASHWORTHINESS AND OTHER SAFETY CONSIDERATIONS 75 considering FAAâs concern about passenger seat cabin interior flammability. Because all wheelchairs must meet WC16 and other standards for everyday usage, wheelchairs labeled as compliant with WC19 will also comply with WC16, and WC19 includes this flammability testing requirement. Before turning to a review of FAAâs safety requirements, differences in the crash environments of airline and motor vehicle transportation are presented in Box 3-3. These differences are important because they underlie key variations in the crash performance test criteria of FAA, with respect to BOX 3-3 Differences Between Motor Vehicle and Airplane Crashes Passenger car crashes and survivable commercial passenger jet airplane crashes can differ in several ways. In the United States in 2018, there were nearly 2 million passenger car crashes in which one or more persons died or was injured (includ- ing pedestrians in some cases).a More than 80 percent of these crashes involved vehicles colliding with one another, about 8 percent involved a vehicle striking a fixed object (e.g., guardrail, pole), about 7 percent involved collisions with nonfixed objects (e.g., parked vehicles), and the remainder did not involve collisions, such as rollovers. Crashes in which the front of the vehicle was the initial point of contact accounted for about half of crashes involving injuries but nearly two-thirds of fatal crashes.b Ensuring the safety of vehicle occupants in frontal collisions is therefore a critical goal of efforts to improve vehicle crashworthiness. Compared with motor vehicle crashes, injuries and fatalities from crashes or other emergencies involving commercial passenger airplanes are exceedingly rare. The main concern for the safety of passenger seating in airplanes is with survivable incidents. Most of these survivable incidents occur during attempted landings or takeoffs. Landing crashes can occur when the airplane lands short of the runway, overruns the runway, leaves the runway to the side, or lands someplace other than the runway.c Takeoff crashes, which are not as frequent as landing crashes, can occur when the airplane leaves the runway, perhaps to the side in strong wind conditions.d Accordingly, crash protection of airplane occupants must take into account vertical forces. Another notable difference between motor vehicle and passenger jet air- plane crashes is that the speed of the airplane on takeoff or landing is typically in the range of 150 to 200 mph, much faster than the speed of a passenger motor vehicle. In addition, in an airplane crash, a large number of passengers may need to be evacuated while the occupants of a motor vehicle are far fewer. a See NHTSA (National Highway Traffic Safety Administration). n.d. âTraffic Safety Facts Annual Report Tables: Table 42.â https://cdan.dot.gov/tsftables/tsfar.htm#. b See NHTSA. n.d. âTraffic Safety Facts Annual Report Tables: Table 43.â https://cdan.dot. gov/tsftables/tsfar.htm. c See, for example, the following National Transportation Safety Board (NTSB) Aircraft Ac- cident Reports (AAR): AAR-16-02, AAR-12-01, AAR-07-06, AAR-01-02, AAR-97-03, AAR-97- 01, and AAR-96-05. https://huntlibrary.erau.edu/collections/aerospace-and-aviation-reports/ ntsb/aircraft-accident-reports. d See, for example, NTSB AAR-10-04. https://libraryonline.erau.edu/online-full-text/ntsb/ aircraft-accident-reports/AAR10-04.pdf.
76 WHEELCHAIR SECUREMENT CONCEPT FOR AIRLINE TRAVEL airplane seats and cabins, and of RESNA, with respect to wheelchairs used as seats in motor vehicles. COMPARISON OF FAA AND RESNA CRASHWORTHINESS CRITERIA As is clear from the discussion above, most FAA Part 25 regulations are performance based; for instance, Â§ 25.561 and Â§ 25.562 specify the forces or accelerations that a seating system must be capable of withstanding without excessive deformation (i.e., to the point where the seat could impede evacuation), but they contain limited direction on how the seat or its structure should be designed. To facilitate compliance with these performance specifications, FAA provides guidance in Advisory Circulars (ACs) on acceptable testing methods. The primary guidance for the Part 25 crashworthiness requirements is AC 25-17A, Transport Aircraft Cabin Interiors Handbook. The AC guidelines on test methods are not mandatory but they are generally followed by airplane manufacturers, modifiers, and type certification engineers because the cost, time, and complexity of dem- onstrating compliance through other testing methods can be prohibitive. In this regard, none of the performance and testing criteria specified by the RESNA WC18 and WC19 standards for demonstrating the crashworthi- ness of WTORS and wheelchairs when used as seats in a motor vehicle can be said to align completely with the FAA Part 25 testing and performance criteria. The differences, of course, are to be expected because the condi- tions of, and concerns associated with, the airplane and motor vehicle crash environments differ as discussed in Box 3-3. With respect to the static testing prescribed by FAA Â§ 25.561, neither WC18 nor WC19 specify that the wheelchair and WTORS complete such static load testing in six directions. Likewise, the RESNA standards do not call for testing under both a vertical dynamic loading condition (14 g) and a longitudinal dynamic loading condition (16 g) as specified by FAA Â§ 25.562 and its criteria for the protection of the seat occupant from head, spinal column, and leg injuries. However, the WC18 and WC19 standards require that a wheelchair and WTORS perform effectively in a frontal crash event creating an average deceleration pulse of 20 g, which bears resemblance to FAAâs longitudinal testing condition inasmuch as both tests are for impacts on a horizontal vector. The RESNA dynamic test is intended to demonstrate that the structural components of the wheelchair do not completely fail, the securement points do not deform in a manner that prevents manual disen- gagement, and the wheelchair remains in an upright position with the oc- cupant remaining in a seated posture. In this regard, the RESNA standards test for the limits of total excursion to minimize the occupantâs impact with stationary objects within a motor vehicle during a crash, but they do
CRASHWORTHINESS AND OTHER SAFETY CONSIDERATIONS 77 not specify occupant injury criteria in the same manner as Â§ 25.562.19 The WC18 and WC19 standards assume that sufficient clear space will be pro- vided in front of the wheelchair so there is less risk of secondary head and leg injuries to a properly belted occupant. Thus, whereas head, torso, and leg injury measures are often collected from the ATD during WTORS and wheelchair testing, they are not used specifically for assessing compliance with WC18 and WC19. How well a WC19-compliant wheelchair and its securement system would perform if tested according to FAAâs two dynamic loading condi- tions is unclear in the absence of comprehensive testing data for a range of wheelchairs and securement system designs suited to airplanes.20 Because WC18 and WC19 do not require a dynamic loading test with a predomi- nantly vertical direction, it is not known how WC19-compliant wheelchairs would perform under this 24-mph, 14-g crash condition, and whether the occupant would be afforded satisfactory protection from spinal injury, as defined by FAA injury criteria. One could surmise, however, that a wheel- chair that performs effectively in the 30-mph, 20-g WC19 frontal crash test could meet FAAâs 16-g longitudinal impact test, perhaps with modest design changes. Both tests follow the horizontal axis but FAAâs test requires the seat to be yawed 10 degrees either right or left (with the wings level), whereas WC19 testing follows the vehicle floorâs horizontal axis. The effect that this yaw condition would have on wheelchair performance, as well as Â§ 25.562âs requirement for testing with misaligned seat tracks, would need to be assessed. However, valid testing of wheelchair crashworthiness according to FAA criteria would also require the use of a securement sys- tem design that could reasonably be expected to be installed in an airplane cabin. WTORS designed for motor vehicle use might suffice, but one would expect systems to be developed that are optimized to perform well under FAA test conditions. Significantly, however, FAAâs criteria for HIC and leg injuries may not be relevant to a wheelchair securement evaluation, under the premise that the wheelchair will be secured in a location with sufficient front and rear clearance so that the occupant of the wheelchair and pas- sengers behind it do not come into contact with hard structures during a high-g event. The size of such a clear space footprint is estimated below and considered further in Chapter 4. As with the dynamic testing criteria, the extent to which RESNAâs WC16 standard for resistance to flammability by a wheelchairâs upholstered surfaces would satisfy FAAâs requirements (in Â§ 25.853) that govern the self-extinguishing capability and flammability of airplane seating systems is difficult to gauge based on side-by-side comparisons of the two sets of 19 And, as noted earlier, for Â§ 25.785âs HIC for safety belt performance. 20 In Chapter 5, some recent, limited testing of aspects of this capability is discussed.
78 WHEELCHAIR SECUREMENT CONCEPT FOR AIRLINE TRAVEL requirements but without testing or other evaluation data. All WC19- compliant wheelchairs must meet WC16, which specifies performance tests for demonstrating the resistance of the wheelchair seating and upholstery materials to ignition by a cigarette and match. While the WC16 testing criteria may provide an indication of the ignition resistance behavior of the wheelchair as a whole, the criteria do not apply to all of the materials that may be used on a fully outfitted, finished wheelchair, including any added or modified cushions for occupant posture, stability, and pressure relief. If such cushions are viewed as an extension of the passengerâs clothing (as they are in WC16), the Â§ 25.853 testing criteria might not apply, but that would be a determination for FAA. With regard to FAA Â§ 25.785âs requirement for seats having energy absorbing arm, shoulder, back, and head rests, WC19 does not contain comparable standards for wheelchairs. There is likewise no WC19 equiva- lent to FAA Â§ 25.785âs requirement for the padding of protruding objects, the benefits of which would presumably be limited to the occupant of the wheelchair if it is properly isolated in the designated securement zone. With regard to FAA Â§ 25.789âs requirement for the retention of items of mass, the WC19 standard requires that rigid components, equipment, and accessories in excess of 150 g do not become detached from the wheelchair during the 20-g frontal impact test. Additionally, the standard requires that wheelchair components that may contact the wheelchair occupant or other nearby occupants do not fragment or separate in a manner that produces sharp edges with a radius of less than 2 mm and that wheelchair batteries stay within the wheelchair footprint, remain attached or tethered to the battery compartment, and do not enter the wheelchair userâs space during the impact event. Nevertheless, because the WC19 dynamic testing criteria, including setup and durations, differ from the dynamic testing criteria in the FAA requirements, it is not possible to make definitive determinations about the likelihood of wheelchair compliance with the latter. As noted above, one would expect that any testing of a wheelchair according to FAA requirements would use a securement system designed to interface effectively with a wide range of wheelchairs but that is also optimized for the airplane operating and crash environments. The fact that WTORS used in motor vehicles are designed to meet WC18âs 20-g dynamic frontal crash test suggests that an effective airplane-specific securement system could be designed, assuming there is sufficient airplane structural strength for its attachments. Like WTORS used in motor vehicles, an airplane-specific securement system would need to be capable of securing a wide range of personal wheelchairs, and thus WC19âs requirement for wheelchairs to have four-point securement brackets would likely remain essential to the design of any initial airplane securement system. Such a system could conceivably be designed with a cabin-anchored occupant
CRASHWORTHINESS AND OTHER SAFETY CONSIDERATIONS 79 restraint system that includes both pelvic and upper torso safety belts; how- ever, if such an installation is not possible, WC19 also prescribes a pelvic belt that can be anchored to the wheelchair. As described earlier, WC19- compliant chairs have been crash tested with a wheelchair-anchored pelvic belt, and pelvic belts without shoulder belts are the norm for conventional airplane passenger seats. Although developed for WTORS used in a motor vehicle securement space, WC18 nevertheless contains helpful guidance for estimating the front and rear clear zones required for an occupied forward-facing wheelchair if secured in an airplane cabin. The desired length of this zone is specified in WC18 to be 950 mm (~36 in.) forward (measured from the front of the occupantâs head when restrained with a pelvic belt) and 500 mm (~20 in.) rearward (measured from the rear of the occupantâs head). This length is established to provide ample clear space to protect the occupant from head and leg injury, while also serving the purpose of providing sufficient room for maneuvering into the securement space, providing footrest and toe space, and enabling wheelchair functionality such as tilting and reclin- ing for occupant posture support and pressure relief. The total distance between the outer limits of the front and rear of the clear-space zone would measure about 60 in., which for a 30-in. wheelchair would create a 30- Ã 60-in. footprint for the securement space.21 Presumably, an airplane-specific securement system could be designed to fit fully within this footprint with sufficient room to secure and release the wheelchair. The analyses and testing that would be required to develop an airplane- specific securement system and any associated standards is outside the scope of this study. Nevertheless, an important question is whether the airplane structure in the securement area would need to be strengthened and other- wise modified to distribute wheelchair static and dynamic loads to primary structure, particularly for occupied power wheelchairs, which are heavier than manual wheelchairs. Because WC18 is intended for WTORS installed in a range of motor vehicles, the relevance of its requirements for anchorage and tiedown point locations may be limited for defining the needs of an in- cabin system. However, in the case of conventional airplane seat assemblies, they are usually attached to seat tracks running fore-aft that are connected to cross beams extending widthwise under the floor. For a narrow-body, mid-size airplane with double-place or triple-place standard seat assemblies, the provision of sufficient clear space for a 30- Ã 60-in. wheelchair secure- ment area could be provided by removing two assemblies, given that the distance between seats (seat pitch) tends to range from about 28 to 42 in. 21 As will be discussed in Chapter 4, this wheelchair securement footprint is consistent with guidelines developed for the Americans with Disabilities Act. The 30- Ã 60-in. space should allow enough room for maneuvering into the space and securing four-point straps.
80 WHEELCHAIR SECUREMENT CONCEPT FOR AIRLINE TRAVEL The removal of these assemblies would also free up floor seat track attach- ment points, which would be needed to provide structural load bearing capacity for a secured wheelchair and securement system. The occupied weight of the wheelchair relevant to the occupied weight of the displaced seat assemblies is therefore an important consideration for assessing whether the removal of two seat assemblies for a securement zone would provide sufficient seat track connections for load bearing ca- pacity. As established in Chapter 2, an occupied power wheelchair could weigh as much as 850 lb, including a 450-lb wheelchair (with battery) and an occupant weighing up to 400 lb.22 When fully occupied with passen- gers, two triple-place seat assemblies are estimated to weigh about 1,200 lb (see Box 3-4); thus, presumably an airplaneâs seats tracks and support structures would be designed to distribute and otherwise safely accommo- date the loads imparted by at least that much weight, which is about 40 percent more than the estimated maximum weight of an occupied power wheelchair. Also, as discussed in Chapter 2, there are systems in common use by airlines, including high-strength and lightweight aluminum pallets, to distribute seat assembly loads across the seat tracks, and presumably similar systems could be engineered and used to distribute the weight of an occupied wheelchair across the seat tracks freed up by two displaced seat assemblies. While it is conceivable that this needed space and structural support could be obtained by removing fewer seats, the assumption that two rows of seats will be displaced is maintained in this chapter.23 Because the location and configuration of seats, galleys, closets, and other floor-mounted components that impart loads can differ across airplane types and interior layouts, it is not possible in this study to make definitive determinations about whether modifications to a given airplaneâs floor and primary structure would be required to accommodate a wheelchair secure- ment system for any given securement location in a cabin. However, in light of the weight calculations above, and knowing that load distribution systems such as pallets are available and in common use for passenger seating, the ability to distribute wheelchair static and dynamic loads would appear to be possible within the norms of interior design and engineering. Indeed, when questioned during briefings to the committee, representatives of airlines and interior component manufacturers expressed confidence that the weight of an occupied wheelchair could be appropriately distributed through com- monly used load distribution means such as seat pallets. Of course, this is a 22 A wheelchair manufacturer briefing the committee indicated that the heaviest fully configured power wheelchairs with batteries can weigh as much as 450 lb and accommodate a 400-lb occupant (Mark Greig, vice president, R&D, Sunrise Medical, August 11, 2020). 23 Typical row seating layouts for airplane models in the U.S. commercial transport fleet (as of December 2019) are included in the Chapter 4 addendum.
CRASHWORTHINESS AND OTHER SAFETY CONSIDERATIONS 81 technical matter that would require more thorough engineering analysis to reach definitive conclusions about floor structural capacity and the viability of using typical systems for load distribution.24 24 In public information-gathering sessions, the committee heard from engineering and other experts from individual airlines, an airplane manufacturer, and airplane seat and cabin interior designers. Hans-Gerhard Giesa and Ralf Schliwa of Airbus stated that there would likely be âno need for changes in aircraft structureâ to accommodate dynamic loads. Raki Islam of SAFRAN Seats and SAFRAN stated, âIt should not be difficult to assign an area of the aircraft that is safe â¦ considering track design, floor strength.â Glenn Johnson of Collins Aerospace stated that it may be âdifficult but not impossibleâ to design concepts to handle floor loading. Giesa, Islam, and Johnson referred to the installation of a pallet in the wheelchair securement area as a way to effectively distribute wheelchair loads to the aircraft; Gregg Fesenmyer of American Airlines also stated that structural loading is a solvable problem. Bryan Parker of Southwest Airlines said that restraining a wheelchair would require adding a plate or pallet to the securement area to transfer dynamic loads, and dynamic testing likely would be needed to certify the wheelchair securement and pallet system together with the wheelchair. BOX 3-4 Estimating Passenger Airplane Seat Weights and Imparted Loads While specific information about airplane seating and other cabin interior products is usually proprietary, estimates of passenger airplane seat assembly weights can be made based on public information provided by seat manufacturers and confirmed by committee members with expertise in airplane interior design. For instance, in an August 2020 Aviation Week article, Mark Hiller, chief executive officer of Recaro Aircraft Seating, one of the three largest commercial aircraft passenger seat suppliers, reported that an economy seat typically weighs 18 to 33 lb.a If one assumes that this range represents a reasonable approxima- tion of typical seat assembly weights, then a triple-seat assembly would weigh between 54 and 99 lb. As noted in this chapter, seats are loaded for FAA testing with a 170-lb dummy in each seat. If 170 lb is considered to be representative of average passenger weight, a fully occupied three-seat assembly would weigh between 564 and 609 lb, and two rows of seats would equate to between 1,128 and 1,218 lb. This range is comparable to the figures used by FAA in the 2005 rulemaking to extend requirements for dynamically tested (16 g) seats to more airplanes. In that rulemaking, FAA estimated that a triple-seat assembly weighs 100 lb and that each occupant weighs 170 lb, resulting in a total assembly weight of 610 lb (or two assemblies weighing 1,220 lb).b a See Dubois, T. 2020. âAircraft Passenger Seat Design Gets Smarter.â Aviation Week, August 14. https://aviationweek.com/mro/interiors-connectivity/aircraft-passenger-seat- design-gets-smarter. b FAA. 2005. âImproved Seats in Air Carrier Transport Category Airplanes: Final Rule.â Federal Register 70, no. 186: 56543.
82 WHEELCHAIR SECUREMENT CONCEPT FOR AIRLINE TRAVEL Finally, the issue of power wheelchair batteries and any hazards that they may create in the cabin will warrant attention, both with regard to a fire hazard and retention of items of mass during an emergency landing or crash. With regard to a fire hazard, most power wheelchairs use lead-acid sealed batteries but other battery types are in use, including nickel metal hydride and lithium ion batteries. The stowage of wheelchairs with these batteries is already allowed by FAA,25 which advises that non-spillable and sealed batteries remain installed on the wheelchair if it is securely at- tached and its housing and terminals are protected from damage and short circuit.26,27 RESNA WC25 contains performance and test criteria and prod- uct labeling for wheelchair batteries, as shown in Figure 3-5. The label can be used as a means of permitting an airline to verify compliance with FAA requirements applicable to battery-powered wheelchairs, whether stowed in baggage holds or secured in the cabin. With regard to batteries being sufficiently secured and retained during an airplane crash or emergency landing, WC19 testing verifies that the 25 45 CFR 175.10. 26 Lithium polymer batteries are growing in popularity, but suitable sizes for power wheel- chair applications can conflict with FAA requirements forbidding lithium batteries with more than 100 watt hours. 27 Industry standards developed by the International Air Transport Association (IATA, in partnership with airlines and the battery industry) address the issues of battery engagement, power activation, and seating function availability when wheelchairs are in the cabin. See IATA. 2021. Battery Powered Wheelchair and Mobility Aid Guidance Document. https:// www.iata.org/contentassets/6fea26dd84d24b26a7a1fd5788561d6e/mobility-aid-guidance- document.pdf. FIGURE 3-5 Label indicating compatibility of battery with RESNA WC25 standards. SOURCE: RESNA.
CRASHWORTHINESS AND OTHER SAFETY CONSIDERATIONS 83 wheelchairâs battery does not become dislodged in a frontal motor vehicle crash. As noted above, WC19âs 20-g frontal crash test bears a resemblance to FAAâs 16-g longitudinal test for airplane seats. Given the higher g load- ing in the WC19 test, this suggests that battery securement might not be an issue at least with respect to crash impacts along the horizontal vector, or potentially one that is minor and could be solved with some modest engineering attention. SUMMARY OF KEY POINTS FAA, which establishes safety and certification standards for passenger airplanes, has not established safety standards that apply to wheelchair se- curement systems or wheelchairs used as seats in airplanes. The main body of FAA regulations that applies to the passenger compartments of airplanes is Title 14 Part 25 of the Code of Federal Regulations (14 CFR 25). These regulations govern airplane seat and cabin interior crashworthiness in a sur- vivable crash or emergency event when the cabin occupants are subjected to forces within human tolerances and the structural integrity of the passenger space remains intact such that the occupants can rapidly evacuate. Voluntary industry standards have been established for the safety of people seated in wheelchairs during motor vehicle transportation. RESNA standards WC18 and WC19 contain performance criteria, test methods, and product labeling for WTORS and wheelchairs used in motor vehi- cles as seats, respectively. The WC19 standard assures that all compliant wheelchairs will have the four designated securement points with specified opening geometry for connecting tiedown straps. The standards require wheelchairs to be tested under dynamic loading that can occur in a frontal motor vehicle crash, specifying that the secured wheelchair be subjected to a 30-mph, 20-g frontal impact test. The tests demonstrate that the structural components of the wheelchair do not fail, the securement points do not deform in a manner that prevents manual disengagement, and the wheel- chair remains in an upright position with the occupant in an upright seated posture at the end of the crash event. There has been no systematic evaluation of wheelchairs and their securement systems regarding their ability to demonstrate satisfactory per- formance with respect to FAAâs crashworthiness criteria for airplane seats, including criteria intended to protect airplane occupants from injury dur- ing survivable crash impacts and emergency landings, resist post-crash fire, and prevent items of mass from becoming loose to create a hazard in the cabin or impede evacuations. The FAA crashworthiness regulations require that airplane seating systems and their occupant restraints perform effec- tively when subjected to testing with multi-directional static and dynamic loadings. The requirements seek to ensure that the seating systems remain
84 WHEELCHAIR SECUREMENT CONCEPT FOR AIRLINE TRAVEL attached to the airplane structure, do not deform to impede evacuation, and protect the occupant from serious injuries. They contain specific criteria for head, spinal, and leg injuries when tested according to the dynamic loading conditions intended to simulate airplane crash scenarios. The dynamic tests also demonstrate that items of mass in the seating system will not break loose to become a hazard in the cabin. Additional FAA requirements for seats and their coverings are intended to reduce the potential for fire by specifying performance criteria for self-extinguishment and fire resistance. Crash protection criteria specified by WC19 are not fully aligned with FAAâs crashworthiness criteria for airplane seating systems and cabin in- teriors, as would be expected because the conditions of, and concerns associated with, the airplane and motor vehicle crash environments differ. Significantly, there are no requirements in WC19 that are comparable to FAAâs multi-directional dynamic force testing of a passenger seat intended to simulate airplane crash conditions and to measure satisfactory protec- tion of the seatâs occupant from injury. WC19âs lack of a vertical direction crash test with associated spinal injury criteria is notable because with the information available it is not possible to know how WC19-compliant wheelchairs would perform when subject to this test intended to simulate a crash in airplane descent. However, when compared to FAAâs longitudinal crash test on a horizontal axis and requiring a peak 16-g loading, WC19âs average 20-g frontal crash test loading may be more exacting than FAAâs peak 16-g longitudinal test, while the lack of head and leg injury criteria in the WC19 test may not be pertinent when the wheelchair is secured in a cabin area and has sufficient clearance from structure and objects to prevent such injuries. All WC19-compliant wheelchairs must meet RESNA standard WC16 for fire resistance; however, FAA fire resistance criteria for passenger seats and cabins are substantially different such that comparative assess- ments are not possible without testing and evaluation data. An important advantage of the RESNA standards is that they establish a baseline minimum level of crash and safety performance that many com- monly used wheelchairs comply with today and that more wheelchairs can be designed to comply with in the future. If the RESNA standards did not exist to provide this common baseline level of safety performance that can be evaluated according to the FAA testing criteria, blanket testing might be required for all individual models of wheelchairs, each having an unknown and potentially wide range of crash performance capabilities. While WC19 compliance does not indicate that a secured wheelchair would satisfy all crashworthiness criteria as required by FAA, it does provide assurance that secured wheelchairs would possess a common set of safety performance characteristics as well as standardized features for securement and occu- pant restraint. The WC19 standard would also provide a defined platform for conducting safety evaluations of wheelchairs used as seats in airplanes,
CRASHWORTHINESS AND OTHER SAFETY CONSIDERATIONS 85 including evaluations conducted for the purpose of strengthening their safety performance in an airplane environment and for supporting decisions by FAA about needed crashworthiness demonstration. Guidance in the WC18 standard for forward-facing wheelchair se- curements in a motor vehicle suggests that a 30- Ã 60-in. securement zone would be needed for a wheelchair used as a seat in an airplane to provide sufficient clear space to protect the occupant from crash injuries sustained from striking objects; maneuver into and from the securement space; and enable tilting, reclining, and other necessary wheelchair adjustments. The wheelchair securement area would require sufficient airplane structural support to distribute the load imparted by an occupied power wheelchair. The removal of two successive rows of airplane seats would accommodate a 30- Ã 60-in. securement zone and free up seat tracks for attachments to structural support sufficient for the secured wheelchair when occupied without necessarily requiring any modifications to airplane struc- ture and by using common methods for seat load distribution.