E9-21299. Special Conditions: Boeing Model 737-600/-700/-700C/-800/-900 and 900ER Series Airplanes; Seats With Inflatable Lapbelts

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Final special conditions; request for comments.

SUMMARY:

These special conditions are issued for Boeing Model 737-600/-700/-700C/-800/-900 and 900ER series airplanes. These airplanes, manufactured by Boeing Commercial Airplanes, will have novel or unusual design features associated with seats with inflatable lapbelts. Special Conditions No. 25-187-SC were issued on October 3, 2001, addressing this issue for the Boeing Model 777 series airplanes. The applicable airworthiness regulations do not contain adequate or appropriate safety standards for this design feature. These special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to that established by the existing airworthiness standards.

DATES:

The effective date of these special condition is August 7, 2009. We must receive your comments by: October 19, 2009.

ADDRESSES:

You must mail two copies of your comments to: Federal Aviation Administration, Transport Airplane Directorate, Attn: Rules Docket (ANM-113), Docket No. NM409, 1601 Lind Avenue, SW., Renton, Washington, 98057-3356. You may deliver two copies to the Transport Airplane Directorate at the above address. You must mark your comments: Docket No. NM409. You can inspect comments in the Rules Docket weekdays, except Federal holidays, between 7:30 a.m. and 4 p.m.

FOR FURTHER INFORMATION CONTACT:

John Shelden, FAA, Airframe and Cabin Safety Branch, ANM-115, Transport Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone [phone] facsimile [phone].

SUPPLEMENTARY INFORMATION:

The FAA has determined that notice of, and opportunity for public comment on, these special conditions are impracticable because these procedures would significantly delay issuance of the design approval and thus delivery of the affected airplanes. In addition, the substance of these special conditions has been subject to the public-comment process in several prior instances with no substantive comments received. The FAA therefore finds that good cause exists for making these special conditions effective upon issuance.

Comments Invited

We invite interested people to take part in this rulemaking by sending written comments, data, or views. The most helpful comments reference a specific portion of the special conditions, explain the reason for any recommended change, and include supporting data. We ask that you send us two copies of written comments.

We will file in the docket all comments we receive, as well as a report summarizing each substantive public contact with FAA personnel concerning these special conditions. You can inspect the docket before and after the comment closing date. If you wish to review the docket in person, go to the address in the ADDRESSES section of this preamble between 7:30 a.m. and 4 p.m., Monday through Friday, except Federal holidays.

We will consider all comments we receive by the closing date for comments. We will consider comments filed late if it is possible to do so without incurring expense or delay. We may change these special conditions in light of the comments we receive.

If you want the FAA to acknowledge receipt of your comments on these special conditions, include with your comments a self-addressed, stamped postcard on which you have written the docket number. We will stamp the date on the postcard and mail it back to you.

Background

On July 8, 2008, Boeing Commercial Airplanes applied for an amendment to type certificate No. A16WE to include the new Boeing Model 737-600/-700/-700C-800/-900 and 900ER series airplanes. These special conditions allow installation of inflatable lap belts for head injury protection on certain seats in Boeing Model 737-600/-700/-700C/800/-900 and 900ER series airplanes. The FAA has issued similar special conditions, No. 25-187-SC and subsequently 25-187A-SC for Boeing Model 777 series airplanes and Special Condition No. 25-148-SC for Boeing Model 767 series airplanes.

The inflatable lapbelt is designed to limit occupant forward excursion if an accident occurs. This will reduce the potential for head injury, thereby reducing the Head Injury Criterion (HIC) measurement, required by Title 14, Code of Federal Regulations (14 CFR), 25.562(c)(5). The inflatable lapbelt behaves similarly to an automotive inflatable airbag, but in this case the airbag is integrated into the lapbelt, and inflates away from the seated occupant. While inflatable airbags are now standard in the automotive industry, the use of an inflatable lapbelt is novel for commercial aviation.

Title 14, Code of Federal Regulations (14 CFR) 121.311(j) requires that no person may operate a transport category airplane type certificated after January 1, 1958, and manufactured on or after October 27, 2009, in passenger-carrying operations, after October 27, 2009, unless all passenger and flight attendant seats on an airplane operated under part 121 meet the requirements of § 25.562 in effect on or after June 16, 1988.

The Boeing Model 737-600/-700/-700C/-800/-900 and 900ER series airplanes, manufactured before October 27, 2009, operated under part 121, are required to show compliance with certain aspects of § 25.562 as specified per Type Certificate No. A16WE. Boeing Model 737-600/-700/-700C/-800/-900 and 900ER series airplanes manufactured on or after October 27, 2009, operated under part 121, must meet all of the requirements of § 25.562 for passenger and flight attendant seats. It is in the interest of installers to show full compliance with § 25.562, so that an operator under part 121 may be able to use the airplane without having to do additional certification work. In addition, some foreign civil airworthiness authorities have invoked these same operator requirements in the form of airworthiness directives.

Occupants must be protected from head injury, as required by § 25.785, by either the elimination of any injurious object within the striking radius of the head, or by padding. Traditionally, this has required a setback of 35 inches from any bulkhead or other rigid interior feature or, where not practical, specified types of padding. The relative effectiveness of these means of injury protection was not quantified. With the adoption of Amendment 25-64 to part 25, specifically § 25.562, a new standard that quantifies required head injury protection was created.

Each seat type design approved for crew or passenger occupancy during takeoff and landing, as required by § 25.562, must successfully complete dynamic tests or be demonstrated by rational analysis based on dynamic tests of a similar type seat. In particular, the regulations require that persons not suffer serious head injury under the conditions specified in the tests, and that protection must be provided or the seat be designed so that the head impact does not exceed a HIC value of 1000 units. While the test conditions described for HIC are detailed and specific, it is the intent of the requirement that an adequate level of head injury protection be provided for passengers in a severe crash.

Because §§ 25.562 and 25.785 and associated guidance do not adequately address seats with inflatable lapbelts, the FAA recognizes that appropriate pass/fail criteria need to be developed that fully address the safety concerns specific to occupants of these seats.

Type Certification Basis

Under the provisions of 14 CFR 21.101, Boeing must show that the Boeing Model 737-600/-700/-700C/-800/-900 and 900ER series airplanes meet the applicable provisions of the regulations incorporated by reference in Type Certificate No. A16WE, or the applicable regulations in effect on the date of application for the change. The regulations incorporated by reference in the type certificate are commonly referred to as the “original type certification basis.” The regulations incorporated by reference in Type Certificate No. A16WE are as follows: Part 25, as amended by Amendment 25-1 through Amendment 25-77, for Boeing Model 737-600, -700, and -800 series airplanes, with the exceptions listed on the type certificate; Title 14 CFR part 25, as amended by Amendment 25-1 through Amendment 25-91, for Boeing Model 737-700C and -900 series airplanes, with the exceptions listed on the type certificate; and part 25, as amended by Amendment 25-1 through Amendment 25-108, for the Boeing model 737-900ER series airplanes, with the exceptions listed on the type certificate.

In addition, the certification basis includes certain special conditions, exemptions, or later amended sections of the applicable parts that are not relevant to these special conditions.

If the regulations incorporating reference do not contain adequate or appropriate safety standards for the Boeing Model 737-600/-700/-700C/-800/-900 and 900ER series airplanes because of a novel or unusual design feature, special conditions are prescribed under § 21.16.

In addition to the applicable airworthiness regulations and special conditions, the Boeing Model 737-600/-700/-700C/-800/-900 and 900ER series airplanes must comply with the fuel vent and exhaust emission requirements of 14 CFR part 34 and the noise certification requirements of 14 CFR part 36.

The FAA issues special conditions as defined in 14 CFR 11.19, in accordance with § 11.38, and they become part of the type certification basis under § 21.17(a)(2).

Special conditions are initially applicable to the model for which they are issued. Should the type certificate for that model be amended later to include any other model that incorporates the same or similar novel or unusual design feature, or should any other model already included on the same type certificate be modified to incorporate the same or similar novel or unusual design feature, the special conditions would also apply to the other model under § 21.101.

Novel or Unusual Design Features

Boeing Model 737-600/-700/-700C/-800/-900 and 900ER series airplanes will incorporate the following novel or unusual design features: seats with inflatable lapbelts.

Discussion

The inflatable lapbelt has two potential advantages over other means of head impact protection. First, it can provide significantly greater protection than would be expected with energy-absorbing pads, and second, it can provide essentially equivalent protection for occupants of all stature. These are significant advantages from a safety standpoint, since such devices will likely provide a level of safety that exceeds the minimum standards of part 25. Conversely, inflatable lapbelts in general are active systems and must be relied upon to activate properly when needed, as opposed to an energy-absorbing pad or upper torso restraint that is passive, and always available. Therefore, the potential advantages must be balanced against this and other potential disadvantages to develop standards for this design feature.

The FAA has considered the installation of inflatable lapbelts to have two primary safety concerns: First, that they perform properly under foreseeable operating conditions, and second, that they do not perform in a manner or at such times as would constitute a hazard to the airplane or occupants. This latter point has the potential to be the more rigorous of the requirements, owing to the active nature of the system.

The inflatable lapbelt will rely on electronic sensors for signaling and pyrotechnic charges for activation so that it is available when needed. These same devices could be susceptible to inadvertent activation, causing deployment in a potentially unsafe manner. The consequences of such deployment must be considered in establishing the reliability of the system. Boeing must substantiate that the effects of an inadvertent deployment in flight are either not a hazard to the airplane, or that such deployment is an extremely improbable occurrence (less than 10⁻⁹ per flight hour). The effect of an inadvertent deployment on a passenger or crewmember that might be positioned close to the inflatable lapbelt should also be considered. The person could be either standing or sitting. A minimum reliability level will have to be established for this case, depending upon the consequences, even if the effect on the airplane is negligible.

The potential for an inadvertent deployment could be increased as a result of conditions in service. The installation must take into account wear and tear so that the likelihood of an inadvertent deployment is not increased to an unacceptable level. In this context, an appropriate inspection interval and self-test capability are considered necessary. Other outside influences are lightning and high intensity electromagnetic fields (HIRF). Existing regulations regarding lightning § 25.1316, HIRF § 25.1317, and HIRF special condition for the Boeing Model 737-600/-700/-700C/-800/-900 and 900ER series airplanes, SC-25-ANM-132, are applicable. For compliance with those conditions, if inadvertent deployment could cause a hazard to the airplane, the inflatable lapbelt is considered a critical system; if inadvertent deployment could cause injuries to persons, the inflatable lapbelt should be considered an essential system. Finally, the inflatable lapbelt installation should be protected from the effects of fire, so that an additional hazard is not created by, for example, a rupture of the pyrotechnic squib.

For an effective safety system, the inflatable lapbelt must function properly and must not introduce any additional hazards to occupants as a result of its functioning. There are several areas where the inflatable lapbelt differs from traditional occupant protection systems, and requires special conditions to ensure adequate performance.

Because the inflatable lapbelt is essentially a single use device, there is the potential that it could deploy under crash conditions that are not sufficiently severe as to require head injury protection from the inflatable lapbelt. Since an actual crash is frequently composed of a series of impacts before the airplane comes to rest, this could render the inflatable lapbelt useless if a larger impact follows the initial impact. This situation does not exist with energy absorbing pads or upper torso restraints, which tend to provide continuous protection regardless of severity or number of impacts in a crash event. Therefore, the inflatable lapbelt installation should be such that the inflatable lapbelt will provide protection when it is required, by not expending its protection during a less severe impact. Also, it is possible to have several large impact events during the course of a crash, but there will be no requirement for the inflatable lapbelt to provide protection for multiple impacts.

Since each occupant's restraint system provides protection for that occupant only, the installation must address seats that are unoccupied. It will be necessary to show that the required protection is provided for each occupant regardless of the number of occupied seats and that unoccupied seats may have lapbelts that are active.

The inflatable lap belt should be effective for a wide range of occupants. The FAA has historically considered the range from the fifth percentile female to the ninety-fifth percentile male as the range of occupants that must be taken into account. In this case, the FAA is proposing consideration of a broader range of occupants, due to the nature of the lapbelt installation and its close proximity to the occupant. In a similar vein, these persons could have assumed the brace position, for those accidents where an impact is anticipated. Test data indicate that occupants in the brace position do not require supplemental protection, so it would not be necessary to show that the inflatable lapbelt will enhance the brace position. However, the inflatable lapbelt must not introduce a hazard when it is deployed into a seated, braced occupant.

Another area of concern is the use of seats, so equipped, by children whether they are lap-held, sitting in approved child safety seats, or occupying the seat directly. Although specifically prohibited by the FAA operating regulations, the use of the supplementary loop belt (“belly belt”) may be required by other civil aviation authorities, and should also be considered with the end goal of meeting those regulations. Similarly, if the seat is occupied by a pregnant woman, the installation needs to address such usage, either by demonstrating that it will function properly, or by adding appropriate limitation on usage.

Since the inflatable lapbelt will be electrically powered, there is the possibility that the system could fail due to a separation in the fuselage. Since this system is intended as crash/post-crash protection means, failure due to fuselage separation is not acceptable. As with emergency lighting, the system should function properly if such a separation occurs at any point in the fuselage.

Since the inflatable lapbelt is likely to have a large volume displacement, the inflated bag could potentially impede egress of passengers. Since the bag deflates to absorb energy, it is likely that an inflatable lapbelt would be deflated when persons try to leave their seats. Nonetheless, it is appropriate to specify a time interval after which the inflatable lapbelt may not impede rapid egress. The maximum time allowed for an exit to open fully after actuation is ten seconds, according to § 25.809(b)(2). Therefore it was chosen as the time interval that the inflatable lapbelt must not impede rapid egress from the seat after it is deployed. In actuality, it is unlikely that an exit would be prepared by a flight attendant this quickly in an accident severe enough to warrant deployment of the inflatable lapbelt. The inflatable lapbelt will likely deflate much quicker then ten seconds.

This potential impediment to rapid egress is even more critical at the seats installed in the emergency exit rows. Installation of the inflatable restraints at the Type III exit rows presents different egress concerns as compared with front row seats. However, the need to address egress is already part of the special conditions so there is no change to the special conditions at this time. As noted below, the method of compliance with the special condition may involve specific considerations when the inflatable restraint is installed at Type III exits. From § 25.813 there are clear requirements that there must be access to the exit from the main aisle in the form of an unobstructed passageway, and no interference in opening the exit. The restraint system must not create an impediment to the access to, and the opening, of the exit. These lap belts should be evaluated in the exit row under existing regulations (§§ 25.809 and 25.813) and guidance material. The inflatable lap belts must also be evaluated in post crash conditions, and should be evaluated using representative restraint systems in the bag deployed condition.

This evaluation would include reviewing the access to and opening of the exit, specifically for obstructions in the egress path, and any interferences in opening the exit. Each unique interior configuration must be considered, e.g., passageway width, single or dual passageways with outboard seat removed, etc. If the restraint creates any obstruction or interference, it is likely that it could impede the rapid egress of the airplane. In some cases, the passenger is the one who will open the exit, such as a Type III over wing hatch. Project specific means-of-compliance guidance is likely necessary if these restraint systems are installed at the Type III exit rows.

Finally, it should be noted that the special conditions are applicable to the inflatable lapbelt system as installed. The special conditions are not an installation approval. Therefore, while the special conditions relate to each such system installed, the overall installation approval is separate, and must consider the combined effects of all such systems installed.

Boeing is proposing to install the following novel or unusual design feature of inflatable lap belts on certain seats of Boeing Model 737-600/-700/-700C/-800/-900 and 900ER series airplanes, to reduce the potential for head injury if an accident occurs. The inflatable lapbelt works similar to an automotive inflatable airbag, except that the airbag is integrated with the lap belt of the restraint system.

The performance criteria for head injury protection in objective terms is stated in § 25.562. However, none of these criteria are adequate to address the specific issues raised concerning seats with inflatable lapbelts. The FAA has therefore determined that, in addition to the requirements of part 25, special conditions are needed to address requirements particular to the installation of seats with inflatable lapbelts.

Accordingly, in addition to the passenger injury criteria specified in § 25.785, these special conditions are proposed for the Boeing Model 737 series airplanes equipped with inflatable lapbelts. Other conditions may be developed, as needed, based on further FAA review and discussions with the manufacturer and civil aviation authorities.

For a passenger safety system, the inflatable lapbelt is unique in that it is both an active and entirely autonomous device. While the automotive industry has good experience with inflatable airbags, the conditions of use and reliance on the inflatable lapbelt as the sole means of injury protection are quite different. In automobile installations, the airbag is a supplemental system and works in conjunction with an upper torso restraint. In addition, the crash event is more definable and of typically shorter duration, which can simplify the activation logic. The airplane-operating environment is also quite different from automobiles and includes the potential for greater wear and tear, and unanticipated abuse conditions (due to galley loading, passenger baggage, etc.). Airplanes also operate where exposure to high intensity electromagnetic fields could affect the lapbelt activation system.

The current Special Conditions for the Boeing Model 777 series airplanes, Special Conditions No. 25-187A-SC, was amended to address flammability of the airbag material. The manufacturer of the inflatable lapbelt was unable to develop a fabric that would meet the inflation requirements for the bag and the flammability requirements of Part I(a)(1)(ii) of appendix F to part 25. The fabrics that were developed that met the flammability requirement did not produce acceptable deployment characteristics. However, the manufacturer was able to develop a fabric that meets the less stringent flammability requirements of Part I(a)(1)(iv) of appendix F to part 25 which has acceptable deployment characteristics.

Part I of appendix F to part 25 specifies the flammability requirements for interior materials and components. There is no reference to inflatable restraint systems in appendix F, because such devices did not exist at the time the flammability requirements were written. The existing requirements are based on both material types, as well as use, and have been specified in light of the state-of-the-art of materials available to perform a given function. Without a specific reference, the default requirement would be for the type of material used to make the inflatable restraint, which is a fabric in this case. However, in writing a special condition, the FAA must also consider the use of the material, and whether the default requirement is appropriate. In this case, the specialized function of the inflatable restraint means that highly specialized materials are needed. The standard normally applied to fabrics is a 12-second vertical ignition test. However, materials that meet this standard do not perform adequately as inflatable restraints. Since the safety benefit of the inflatable restraint is very significant, the flammability standard appropriate for these devices should not screen out suitable materials and thereby effectively eliminate the use of inflatable restraints. The FAA will need to establish a balance between the safety benefit of the inflatable restraint and its flammability performance. Right now, the 2.5-inch per minute horizontal test is considered to provide that balance. As the state-of-the-art in materials progresses (which is expected), the FAA may change this standard in subsequent special conditions to account for improved materials.

The following special conditions can be characterized as addressing either the safety performance of the system, or the system's integrity against inadvertent activation. Because a crash requiring use of the inflatable lapbelts is a rare event, and because the consequences of an inadvertent activation are potentially quite severe, these latter requirements are probably more rigorous from a design standpoint.

Applicability

These special conditions are applicable to the Boeing Model 737-600/-700/-700C/-800/-900 and 900ER series airplanes. Should Boeing apply at a later date for a change to the type certificates to include another model that incorporates the same novel or unusual design feature, or should any other model already included on the same type certificate be modified to incorporate the same or similar novel or unusual design feature, the special conditions would also apply to the other model as well.

Conclusion

This action affects only certain novel or unusual design features on the Boeing Model 737-600/-700/-700C/-800/-900 and 900ER series airplanes. It is not a rule of general applicability, and it affects only Boeing Model 737-600/-700/-700C/-800/-900 and 900ER series airplanes listed on Type Certificate No. A16WE.

List of Subjects in 14 CFR Part 25

• Aircraft
• Aviation safety, reporting and recordkeeping requirements

The authority citation for these special conditions is as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

The Special Conditions

Accordingly, pursuant to the authority delegated to me by the administrator, the following special conditions are issued as part of the type certification basis for the Boeing Model 737-600/-700/-700C/-800/ and 900ER series airplanes with inflatable lapbelts installed.

1. Seats With Inflatable Lapbelts

It must be shown that the inflatable lapbelt will deploy and provide protection under crash conditions where it is necessary to prevent serious head injury. The means of protection must take into consideration a range of stature from a two-year-old child to a ninety-fifth percentile male. The inflatable lapbelt must provide a consistent approach to energy absorption throughout that range of occupants. In addition, the following situations must be considered:

a. The seat occupant is holding an infant.

b. The seat occupant is a child in a child restraint device.

c. The seat occupant is a child not using a child restraint device.

d. The seat occupant is a pregnant woman.

2. The inflatable lapbelt must provide adequate protection for each occupant regardless of the number of occupants of the seat assembly, considering that unoccupied seats may have active seatbelts.

3. The design must prevent the inflatable lapbelt from being either incorrectly buckled or incorrectly installed such that the inflatable lapbelt would not properly deploy. Alternatively, it must be shown that such deployment is not hazardous to the occupant, and will provide the required head injury protection.

4. It must be shown that the inflatable lapbelt system is not susceptible to inadvertent deployment as a result of wear and tear, or inertial loads resulting from in-flight or ground maneuvers (including gusts and hard landings), likely to be experienced in service.

5. Deployment of the inflatable lapbelt must not introduce injury mechanisms the seated occupant, or result in injuries that could impede rapid egress. This assessment should include an occupant who is in the brace position when it deploys and an occupant whose belt is loosely fastened.

6. It must be shown that an inadvertent deployment, that could cause injury to a standing or sitting person, is improbable.

7. It must be shown that inadvertent deployment of the inflatable lapbelt, during the most critical part of the flight, will either not cause a hazard to the airplane or is extremely improbable.

8. It must be shown that the inflatable lapbelt will not impede rapid egress of occupants 10 seconds after its deployment.

9. The system must be protected from lightning and HIRF. The threats specified in existing regulations regarding lightning, § 25.1316, HIRF, § 25.1317, and existing HIRF special conditions for the Boeing Model 737-600/-700/-700C/-800/-900 and 900ER series airplanes, SC-25-ANM-132, are incorporated by reference for the purpose of measuring lightning and HIRF protection. For the purposes of complying with HIRF requirements, the inflatable lapbelt system is considered a “critical system” if its deployment could have a hazardous effect on the airplane; otherwise it is considered an “essential” system.

10. The inflatable lapbelt must function properly after loss of normal aircraft electrical power, and after a transverse separation of the fuselage at the most critical location. A separation at the location of the lapbelt does not have to be considered.

11. It must be shown that the inflatable lapbelt will not release hazardous quantities of gas or particulate matter into the cabin.

12. The inflatable lapbelt installation must be protected from the effects of fire such that no hazard to occupants will result.

13. There must be a means for a crewmember to verify the integrity of the inflatable lapbelt activation system prior to each flight or it must be demonstrated to reliably operate between inspection intervals.

14. The inflatable material may not have an average burn rate of greater than 2.5 inches/minute when tested using the horizontal flammability test as defined in 14 CFR part 25, appendix F, part I, paragraph (b)(5).

Issued in Renton, Washington, on August 7, 2009.

Stephen P. Boyd,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.