Advisory U.S. Department of Transportation Federal Aviation Circular Administration Subject: Dynamic Evaluation of S eat Restraint Date: AC No: 25.562-1B Systems and Occupant Protection on Transport Initiated By: ANM-115 Change: 1 Airplanes
1. PURPOSE.
a. This change removes guidance in paragraph 5e(5)(d) of AC 25.562-1B, which allowed certain methods for showing compliance with the head injury criterion (HIC) required by Title 14, Code of Federal Regulations (14 CFR) 25.562(c)(5). These methods were issued in error and have resulted in conditions where the full required range of occupants might not have the same level of head injury protection. These methods also conflict with Federal Aviation Administration (FAA) Policy Memorandum ANM-115-05-14, Policy Statement on Acceptable Methods of Compliance with § 25.562(c)(5) for Front Row Passenger Seats, dated December 14, 2005, for showing compliance with HIC for front row seats. This change eliminates that conflict. An acceptable simplified method for a showing of compliance with HIC for row-to-row seats continues to be the method described in Appendix 4 of this advisory circular (AC) and our policy. We have also added a note for front row seats clarifying how to apply guidance for the 42"/45" setback criteria. Further, we have deleted a reference to canceled AC 25-17 that is no longer relevant and fixed typographical errors within the AC.
b. This change also clarifies applicability of Appendix 4 to seats containing upper torso restraints and airbags; clarifies the range of yaw angles that an applicant should address; and adds guidance for front row seats.
2. PRINCIPAL CHANGES. Change 1 updates AC 25.562-1B, Dynamic Evaluation of Seat Restraint Systems and Occupant Protection on Transport Airplanes, dated January 10, 2006. We have added the change number and date of revision at the top of each changed page. We have also marked the changes with a vertical change bar in the margin. Specifically, Change 1 incorporates the following changes:
a. Corrects the figure references in Steps 3 and 3d under paragraph 5d(1).
b. Corrects typographical errors in the second question of Figure 5-2. We also redesigned the figure to improve readability.
c. Adds guidance for upper torso restraints and airbags to the end of paragraph 5e(5)(a) and paragraph 1 of Appendix 4.
d. Clarifies guidance on the range of yaw angles and specifies that a solid strike must be used to show compliance for the range of occupants in paragraph 5e(5)(b).
e. Deletes paragraph 5e(5)(d) and the bulleted list of items that follow it. This is the change that removes the erroneous guidance.
f. Redesignates paragraph 5e(5)(e) as paragraph 5e(5)(d).
g. Adds guidance for limiting the range of occupants to the end of redesignated paragraph 5e(5)(d).
h. Adds new paragraph 5e(5)(d)1 for a test with bulkhead method and glancing blow acceptance.
i. Redesignates the two bulleted paragraphs under paragraph 5e(5)(e) as paragraphs 5e(5)(d)2 and 5e(5)(d)3, respectively.
j. Adds a reference to redesignated paragraph 5e(5)(d)2 specifying where in the AC one can find additional guidance.
k. Deletes the last sentence of redesignated paragraph 5e(5)(d)2.
l. Adds a note under redesignated paragraph 5e(5)(d)2.
m. Corrects the figure reference in paragraph 6e.
n. Corrects the figure reference in paragraph 9c(5)(a)1 and 2.
o. Corrects the figure references in paragraph 10e(3).
p. Corrects a typographical error in paragraph 11b(2) of Appendix 3.
q. Corrects a typographical error in paragraph 11c of Appendix 3.
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Jeffrey E. Duven Manager, Transport Airplane Directorate Aircraft Certification Service
Advisory Circular
Subject: Dynamic Evaluation of Seat Date: 01/10/06 AC No: 25.562-1B Restraint Systems and Occupant Initiated by: ANM-110 Protection on Transport Airplanes
1. PURPOSE. This advisory circular (AC) provides information and guidance regarding acceptable means of compliance with the requirements of 14 CFR part 25 applicable to dynamic testing of seats. The AC provides background and discussion of the reasoning behind the test procedures. It also describes the test facilities and equipment necessary to conduct the tests.
2. APPLICABILITY.
a. The guidance provided in this document is directed to airplane manufacturers, modifiers, foreign regulatory authorities, Federal Aviation Administration (FAA) transport airplane type certification engineers, and FAA designees.
b. This material is neither mandatory nor regulatory in nature and does not constitute a regulation. It describes accepta ble means, but not the only means, for demonstrating compliance with the applicable regulations. The FAA will consider other methods of demonstrating compliance that an applicant may elect to present While these guidelines are not mandatory, they are derived from extensive FAA and industry experience in determining compliance with the relevant regulations. On the other hand, if we become aware of circumstances that convince us that following this AC would not result in compliance with the applicable regulations, we will not be bound by the terms of this AC, and we may require additional substantiation or design changes as a basis for finding compliance.
c. This material does not change or create any additional regulatory requirements nor does it authorize changes in, or permit deviations from, existing regulatory requirements.
3. CANCELLATION. Advisory Circular 25.562-1A , dated 01/19/96, is canceled.
4. RELATED REGULATIONS. Sections 25.562, 25.785, 25.787, and 25.789 of Title 14, Code of Federal Regulations.
Ali Bahrami Manager Transport Airplane Directorate Aircraft Certification Service ii
a. General
e.
Injury Criteria
f. Deformation for Egress
a.
General
AC 25.562-1B 01/10/2006
CONTENTS
SECTION PAGE
1. DEFINITIONS 1
2. DISCUSSION 2
a. Intent of Tests 2
b. Standardized Test Procedures—Reasons a nd Practicalities 2
c. Standardized Test Procedures—Relationship to Design 2
3. TEST CONDITIONS 4
a. General 4
b. Consideration of Test Criteria 7
4. TEST ARTICLES 8 8
b. Critical Components 8
c. Family of Seats 9
5. TEST ARTICLE SELECTION AND RELATED TEST SETUP 10
a. General 10
b. Criteria for Selection 11
c. Family of Seats 11
d. Structural Tests 11 16 20
6. TEST FACILITIES 21
a. General 21
b. Deceleration Sled Facilities 21
c. Acceleration Sled Facilities 22
d. Impact-with-rebound Sled Facilities 23
e. Drop Towers 23
7. ANTHROPOMORPHIC TEST DEVICES 24
a. General 24
b. Modification to Measure Pelvic/Lumbar Load 24
c. Other ATD Modifications 25
d. Equivalent ATDs 26
8. INSTRUMENTATION 26 26
b. Electronic Instrumentation 27
c. Photographic Instrumentation 28 iii
9. TEST FIXTURES 29
a. General 29
b. Floor Deformation 29
c. Other Mounting Configuration Constraints 31
d. Side-facing Seats 38
e. Multiple Row Test Fixtures 38
f. Other Fixture Applications 39
10. TEST PREPARATION 39
a. Preparation for the Tests 39
b. Use of Anthropomorphic Dummies 39
c. Seat Adjustment 40
d. Installation of Instrumentation 40
e. Restraint System Adjustment 41
f. Floor Requirement 42
g. Seat Components 42
11. DATA REQUIREMENTS 45
12. DATA ANALYSIS 45
a. General 45
b. Impact Pulse Shape 46
c. Total Velocity Change 47
d. Head Injury Criterion (HIC) 47
e. Upper Torso Restraint System Load 48
f. Compressive Load Between the Pelvis and Lumbar Column 48
g. Retention of Upper Torso Restraint Straps 49
h. Retention of Pelvic Restraint 49
i. Femur Load 49
13. PASS/FAIL CRITERIA 49
14. TEST FAILURES VS. RETEST 50
15. TEST DOCUMENTATION 51
a. General 51
b. Test Description 52
16. COMPUTER MODELS 53
iv
APPENDICES APPENDIX 1 – PROCEDURES FOR EVALUATING PULSE SHAPES 55 APPENDIX 2 – SEAT DEFORMATION 60 APPENDIX 3 – SEAT FAMILY DEFINITION 64 APPENDIX 4 – DEMONSTRATING COMPLIANCE WITH HIC FOR 86
REPETITIVE SEAT ROWS APPENDIX 5 – SUBSTANTIATING RETENTION OF ITEMS ATTACHED 94
TO SEATS
FIGURES Figure 3-1 – Seat/Restraint System Dynamic Tests 6 Figure 5-1 – Decision Chart – 16g Test 13 Figure 5-2 – Structural Test Article Decision Tree for Seat Family 14 Figure 5-3 – Restraint Trailing Occupant 18 Figure 7-1 – Installation of Pelvic-Lumbar Load Cell in Part 572B ATD 25 Figure 9-1 – Schematic Floor Deformation Fixture – Seat Legs Attached 30 at Floor Level Figure 9-2 – Floor Warpage Multiple Leg Seat 32 Figure 9-3 – Floor Warpage Multiple Leg Seat 33 Figure 9-4 – Schematic Floor Deformation Fixture – Seat Legs Attached 36 at Side Wall Figure 9-5 – Seats Mounted in an Aisle 37 Figure 10-1 – Measurement of 1g Pre-load 43 Figure 10-2 – Test Orientation, 1g Position 44 v
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1. DEFINITIONS. The following definitions apply to the terms used in this AC.
These terms may be used in other documents with different meanings and should, therefore, be verified in the context of those documents.
Anthropomorphic Test Device (ATD)—A device—sometimes called a test “dummy”— used to provide realistic dynamic response representing that of a human.
Baseline Testing—The initial series of tests performed as part of the original certification to substantiate that a family of seats meets regulatory requirements.
Energy Absorbing Device—An energy dissipating element of a seat which is load-rate or peak-load sensitive.
Energy Absorber “Bottom-Out”—The energy absorber “bottoms out” when it reaches its maximum stroke and no longer provides an energy absorption function.
Energy Absorber Rating—The load required to actuate the energy-absorbing device. The “highest rated” energy-absorbing device would be the device that requires the highest load to initiate.
Family of Seats—A group of seat assemblies, regardless of the number of seat places, built from equivalent components in the primary load path. See paragraph 4c and Appendix 3 for an expanded discussion.
Instability Failure—An instantaneous loss of the load-carrying capability of a structural member (for example, the collapse of a column).
Occupant Position—The static relationship of the occupant relative to fixed points on the seat. This is assessed using the Seat Reference Point (SRP), as defined in Society of Automotive Engineers Aerospace Standard AS8049 Revision A.
Rational Analysis—An analysis based on good engineering principles, judgment, and/or accepted methodology. This can include, but is not limited to, static/dynamic load comparison, static strength analysis, comparative static/dynamic strength analysis, linear static and non-linear finite element analysis, and inspection.
Seat Primary Load Path—The components within the seat that carry the load from the point of load application to the structure that reacts the load from the seat system or subsystem. The primary load path may be segmented into its discrete elements, depending on the parameter being evaluated, as follows:
• Structural: from seat belt to fittings which attach the seat system to the airplane structure.
• Lumbar: from bottom cushion to fittings which attach the seat system to the airplane structure.
• Row-to Row Head Injury Criterion (HIC): from point of ATD head contact to the attachment of seat primary structure.
• Head Path (for example, front row or large pitch seats): same as structural.
Similar Design Philosophy - A design which uses the same:
• Method of construction and manufacturing process (for example, machined part versus built-up part),
• Detail part materials (for example, alloys or heat treat),
• Load path,
• Geometry, including section properties, except for minor differences resulting from space limitations within the seat or aircraft interface, and
• Attachment method, except for minor differences resulting from space limitations within the seat Typically—to be considered “minor”—differences to the geometry and attachment method must be shown to be equivalent to or less critical than the seat tested during “baseline testing” with regard to strength, stiffness, and seat permanent deformation.
2. DISCUSSION.
a. Intent of Tests. The intent of the tests is to ev aluate airplane seats, restraints, and related interior systems in order to demonstrate their structural strength and their ability to protect an occupant from serious injuries in a survivable crash. For example, the potential for serious head injury, which is influenced by head strike envelopes and seat pitch, is assessed in the tests. A standardized methodology for making head impact injury assessments is provided in Appendix 4. This methodology should minimize the amount of testing required.
b. Standardized Test Procedures—Reason and Practicalities. The tests described in this AC are standardized procedures generally regarded as the minimum necessary to demonstrate compliance. Standardized procedures seek to obtain consistent results between different test facilities. These faciliti es may be of varying types, as described in paragraph 6. Often they are not under the direct control of the de signer or manufacturer of the article under test, and they may be primarily dedicated to testing which is not related to the aerospace industry. To foster industry standardization, this AC describes many of the procedures and evaluations that are already accepted as standards by government and commercial test facilities. Th ese procedures have been modified only as necessary for the specific testing of civil airplane systems.
c. Standardized Test Procedures—Relationship to Design. As stated above, the tests are standardized by necessity. However, the seat/res traint should be designed to protect the occupant under all conditions within the impact envelope specified in § 25.562.
(1) Occupant representation. The dynamic tests are performed with an anthropomorphic test device (ATD)—representing approximately the 50th percentile male occupant—in accordance with 49 CFR part 572.
(a) Occupant Weight. Although th e basic structural capability of the seat/restraint system is not demonstrated for occupants of other weights, substantiating the seat using the 50th percentile ATD protects the widest range of occupants. Seats that are optimized for occupants at either extreme would have stiffness characteristics that would be incompatible with occupant mass at the other extreme. That is, such seats would either be too stiff to absorb energy for lighter occupants or too flexible to provide protection for heavier occupants.
(b) Occupant Size (dimensions). Th e seat should not be point-designed around the 50th percentile occupant size. The designer should consider other design factors that are directly influenced by occupant size, such as energy absorbing systems, restraint system design and anchorage locations, and seat adjustments.
(2) Test conditions. This AC describes two basic types of dynamic test procedures (see Figure 3-1): a test where the predominant impact vector is vertical and a test where the dominant impact vector is horizontal. These procedures address the tests required to demonstrate compliance for one seat and restraint system installation.
Typical use of a seat model on a particular airplane will involve variations of seat design and installation. Additional tests may be necessary to demonstrate compliance for these variations, if they cannot be adequately addressed by analysis. This point is discussed at length in paragraph 5, and a methodology for establishing a seat “family” is described in Appendix 3.
(3) Pre-test floor deformation. For certain structural evaluations, the test procedure requires that the seat/floor interface should be deformed. This procedure provides a measure of the seat’s ability to deform and absorb energy during an impact.
The seat and restraint system should also perform properly, if the floor remains undeformed.
(4) Head impact. Occupant head impact with th e interior of the airplane is evaluated by using a Head Injury Criterion (HIC) that can be measured directly in the tests described in this AC or in alternative tests. The HIC is measured on the most critical surface within the ±10 degrees yaw envelope (measurement of the HIC does not supersede the requirements of § 25.785, which may have a different head strike envelope than § 25.562). The HIC does not evaluate inju ries that occur at low impact velocities from contact with surfaces having small contact areas or sharp edges, especially if those surfaces are relatively rigid. These types of injuries require assessment in accordance with § 25.785.
(5) Femur injury. Extensive seat testing has shown that the femur loading criterion is not exceeded when seats are tested in accordance with the conditions defined in this AC. For this reason, the femur loads need not be recorded in the individual test, if 3