ABSTRACT

            A series of side facing seat impact sled tests were conducted using the SID, EuroSID-1 and BioSID side impact Anthropomorphic Test Dummies  (ATDs) at the FAA Civil Aeromedical Institute (CAMI).  The tests were performed on a side facing sofa fixture with a rigid bulkhead adjacent to the forward end of the seat.  The purpose of the research project was to examine the methods utilized by the automobile industry to assess thoracic injuries due to side impact accidents, and to investigate the potential applicability of these methods for side facing seats and sofas in civil aircraft.  Tests were conducted with single and double occupants.   The test conditions complied with the 16g 44 f/s horizontal impact specified in 14 CFR 25.562.  Various side impact injury criteria were evaluated in the tests, including the Thoracic Trauma Index (TTI), Viscous Criteria (VC), rib deflection and pelvis acceleration.  Analysis of the data acquired from the tests and observations related to injury parameters from the three ATDs are presented.  Seating and restraint system configurations that indicated potential improvements in occupant protection for side facing seats were also identified.

INTRODUCTION

            One of the objectives of FAA’s regulations for dynamic seats is to provide occupant protection from the serious injuries most likely to occur as the result of a survivable accident.  The regulation applies to all seats occupied during takeoff or landing, including side facing seats and sofas.   The injury criteria specified in regulation 14 CFR 25.562 were developed with the primary focus on forward facing seats.  No specific guidelines for the certification of side facing seats are included in the pass/fail criteria published in the regulation. 

            FAA’s Advisory Circular (AC) 25.562 prescribes test procedures and documentation that are considered as acceptable means of compliance with the regulation for dynamic seats in transport category aircraft.  The AC states:   "The injury criteria of 14 CFR 25.562 are not adequate to demonstrate the equivalent safety of side facing seats. To demonstrate equivalent safety fully in the absence of such specified criteria, the applicant must use other injury criteria which may be derived from the automotive industry, which uses side impact anthropomorphic test devices or dummies (ATDs)."   The AC does not specify a method of compliance nor the injury pass-fail criteria for side facing seats.

            Another relevant regulation, 14 CFR 25.785, mandates: "Each seat, berth, ...designated as occupiable during takeoff and landing must be designed so that a person making proper use of these facilities will not suffer serious injury in an emergency landing as a result of the inertia forces specified in §25.561 and §25.562."  In order to provide a level of protection consistent with forward facing seats, it may be necessary to consider potential serious injuries unique to the side facing seat environment.

            It is important to note that, although AC 25.562 suggests the use of criteria from the automotive industry, the situation for aircraft side facing seats is quite different from the automotive side impact protection environment.  Automobile side impact protection is based on an accident scenario involving a stationary vehicle being struck on the door by another vehicle.  The force of the impact on the door results in deformation and intrusion of the door into the passenger compartment.  The side impact ATD seated adjacent to the struck door is exposed to the forces and energy from the encroachment of the door structures. 

            Aircraft seat dynamic performance is evaluated by a test procedure that exposes the seat, ATD, and proximal structures to an impact pulse.  There is no requirement to evaluate the effects of fuselage intrusion.  Thus, contact injuries are assessed by the flail motion of the ATD as it strikes a seat back, instrument panel, wall, or other furnishing included in the dynamic test.

The purpose of the research presented in this report is to evaluate the various injury assessment methods available with automobile side impact ATDs, when tested by the methods prescribed for aircraft seats.  Comparison of the responses and injury criteria measured from the distinctly different ATDs may indicate whether any (or all) of the ATDs provide results that could be used to establish performance standards for side facing seats in airplanes.  

 SIDE IMPACT ATDS AND INJURY CRITERIA

            The side impact ATDs used by the automotive industry in dynamic testing includes Side Impact Dummy (SID), European Side Impact Dummy (EuroSID-1) and Biofidelic Side Impact Dummy (BioSID).  A comparison between these three ATDs outlining their important features is made in Table 1.  Figure 1 shows the instrumentation of the side impact ATDs. 

Table 1.  Comparison of side impact ATDs – (SID, EuroSID-1 and BioSID)

SID                                                            EuroSID-1                                                BioSID

Figure 1.  Side Impact ATDs instrumentation

The automotive industry has developed injury criteria that are used to evaluate the potential for occupant injuries in automobile side impact accidents.  Several of these injury criteria have been adopted as regulatory requirements by the government authorities for automobile regulations of various countries. Others have been used solely for research purposes.  In the US, the SID ATD is specified in 14 CFR 572 subpart F, and the side impact test requirements for automobiles is defined in 14 CFR 214 (which is commonly referred to as Federal Motor Vehicle Safety Standard 214, or FMVSS-214).  These injury criteria warrant careful examination to determine if they may be useful as a means of evaluating potential injuries in side facing aircraft seats.  A comprehensive list of these potential injury criteria are listed in the following:

The potential for pelvis fracture is evaluated by measuring the lateral acceleration of the pelvis.  This acceleration must not exceed 130 G's.

The TTI is an acceleration-based criterion, which is based on the maximum value of the nearside rib and spinal accelerations, irrespective of differences in time of occurrence, to determine an average acceleration response of the ATD. The Thoracic Trauma Index, TTI, as measured by a side impact ATD should not exceed 85g.  This limit corresponds to AIS (Abbreviated Injury Scale) of 3, which is indicative of serious injury to the thoracic region.  The formula for calculating TTI is:

TTI = ˝ (RIB_G + T12_G)

Where: 
RIB_G is the larger of the peak acceleration of the upper or the lower rib (chest) in G's,
T12_G is the peak acceleration of the 12 thoracic or the lower spine in G's.

VC is evaluated from the product of the velocity of deformation and the instantaneous compression of the chest region of ATD.

V*C =

Where:
D is deflection of the rib(s) or chest,
 is velocity of deformation of the rib(s) or chest,
T_o is half of undeformed width of the torso or chest.

(V*C) is a measure of the soft tissue injury induced by excessive deformation of the chest. It is rate sensitive and corresponds to potential injuries that are not addressed by compression criteria. 

The lateral compression of rib-to-spine deformation should not exceed 1.6-in. (42 mm).

As measured by the EuroSID-1 ATD, not to exceed 2,250 lb. (10 KN).

As measured by the EuroSID-1 ATD, not to exceed 560 lb. (2.5 KN).

As measured by BIOSID or Hybrid III, not to exceed 354 in-lb. (40 N-m).

As measured by BIOSID or Hybrid III, not to exceed 250 lb. (1.1 KN).

HIC shall not exceed 1000. It is defined as 

Where:        

a(t) is the instantaneous resultant acceleration of head CG in G's, and
t₁ and t₂ are times in the pulse which maximize the HIC value.

Measured between the pelvis and the lumbar column not to exceed 1,500 lb. (7 KN).

The axial compressive load in each femur of the ATD shall not exceed 2,250 lb. (10KN).

For a three-point restraint system, the tension in the shoulder strap must not exceed 1,750 lb. (7.8 KN).

SIDE FACING SEAT RESEARCH PROGRAM

            The rational used to develop the test protocol is shown in the Figure 2, and a summary test matrix is presented in Table 2.  A preliminary test series was conducted to study occupant kinematics and establish a baseline for occupant modeling. The results of these tests indicated that the following conditions required further study:

1.       Occupant interaction with a barrier (Test # A96107).
2.       Occupant to occupant interactions (Test # A96108).
3.       The effect of padding on the barrier (Test # A96123).

           A preliminary model was then developed by the National Institute for Aviation Research using the occupant simulation software MADYMO to arrive at the test matrix.  A series of sled tests were conducted based on this at CAMI.  The dynamic side facing seat tests were conducted at CAMI using their horizontal deceleration type impact sled, shown schematically in Figure 3.  A typical deceleration pulse is shown in Figure 4.