[Federal Register Volume 62, Number 100 (Friday, May 23, 1997)]
[Rules and Regulations]
[Pages 28315-28318]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-13588]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM-133; Special Conditions No. 25-ANM-127]


Special Conditions: Jetstream Aircraft Limited, Jetstream Model 
4100 Series Airplanes, Passenger Airbag Installation

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are to be issued to Jetstream 
Aircraft Limited of Prestwick, Scotland (formerly British Aerospace 
Public Limited Company (BAe)) for the Jetstream Model 4100 series 
airplanes. This airplane series has a novel or unusual design feature 
associated with the installation of passenger airbags. Since the 
applicable airworthiness regulations do not contain adequate or 
appropriate safety standards for this particular design feature, these 
special conditions contain the additional safety standards which the 
Administrator finds necessary to establish a level of safety equivalent 
to that established by the airworthiness standards for transport 
category airplanes.

EFFECTIVE DATE: June 23, 1997.

FOR FURTHER INFORMATION CONTACT: Jeff Gardlin, Regulations Branch, ANM-
114, Transport Airplane Directorate, Aircraft Certification Service, 
FAA, 1601 Lind Avenue SW., Renton, Washington 98055-4056; telephone 
(206) 227-2136.

SUPPLEMENTARY INFORMATION:

Background

    On May 24, 1989, BAe Public Limited Company (currently Jetstream 
Aircraft Ltd.) applied for a type certificate for the BAe Model 4100 
(currently Jetstream Model 4101) airplane in the transport airplane 
category. The Model 4100 is a derivative of the Model 3100, which is a 
small airplane as defined by 14 CFR part 1, and is certificated under 
the provisions of 14 CFR part 23. Like the Model 3100, the Model 4100 
was a low wing, twin engine turbo-prop design. The FAA issued Type 
Certificate (TC) A41NM for the Jetstream Model 4101 airplane on April 
9, 1993. The TC includes Exemption 5587 from compliance with the head 
injury criteria (HIC) requirements in 14 CFR Sec. 25.562 for the front 
row of passenger seats.
    Section 25.562 specifies that dynamic tests must be conducted for 
each seat type installed in the airplane. The pass/fail criteria for 
these seats include structural as well as human tolerance criteria. In 
particular the regulations require that persons not suffer serious head 
injury under the conditions specified in the tests, and that a HIC 
measurement of not more than 1000 units be recorded, should contact 
with the cabin interior occur. The HIC is based on physiological data, 
and was first introduced in the automotive industry. At the time the 
rule was written, compliance with the HIC requirement was expected to 
involve using energy absorbing pads, upper torso restraints, or 
increasing spacing between seats and interior features. In

[[Page 28316]]

the years following publication of the rule, the requirement has proven 
difficult to comply with using ``conventional'' means, and there has 
been commercial resistance to installation of upper torso restraint for 
passengers. Because of the technical problems, BAe and other 
manufacturers were granted temporary exemptions to allow certification 
of their airplanes while design solutions were developed.
    One design solution that appeared to be impractical early in its 
adaptation to aircraft was airbags, even though airbags are widely used 
in automobiles as a supplemental restraint system. While the service 
history in automobiles is quite good, the operating environment and 
conditions of use in aircraft are quite different from automobiles. The 
FAA will not enumerate the differences here, but they include exposure 
to electromagnetic fields, wear and tear considerations, crash sensing 
systems etc., and did serve to help frame the content of the special 
conditions. In any case, airbags were not envisioned as a means of 
compliance with the FAR, and the rules are not adequate to define the 
necessary criteria. Therefore, special conditions are necessary.
    Airbags have two potential advantages over other means of head 
impact protection. They essentially provide equivalent protection for 
all sizes of occupants and they can provide significantly greater 
protection than would be expected with energy absorbing pads, for 
example. These are significant advantages from a safety standpoint, 
since airbags will likely provide a level of safety that exceeds the 
minimum standards of the Federal Aviation Regulations (FAR). 
Conversely, airbags are an active system, and must be relied upon to 
activate properly when needed, as opposed to an energy absorbing pad or 
upper torso restraint that is always available. These potential 
advantages must be balanced against the potential problems in order to 
develop standards that will provide an equivalent level of safety to 
that intended by the regulations.
    The FAA has considered the installation of airbags 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. With this philosophy in mind, the FAA has considered the 
following as a basis for the special conditions.
    The airbag 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. For example, there is subjective evidence that there may be 
transient overpressure (shock) caused by deployment of the airbag. 
Jetstream 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 that might be positioned close to the airbag 
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. For example, an airbag installed in a 
galley wall or windscreen will be subjected to wear and tear associated 
with loading the galley and rough contact from baggage during aircraft 
boarding, etc. Whether or not these conditions are more severe than in 
the automotive world, 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 high intensity electromagnetic fields and 
lightning. Since the sensors that trigger deployment are electronic, 
they must be protected from the effects of these threats. Existing 
Special Conditions No. 25-ANM-48 are therefore incorporated by 
reference. For the purposes of compliance with those special 
conditions, if inadvertent deployment could cause a hazard to the 
airplane, the airbag is considered a critical system; to the extent 
that injuries to persons could result from inadvertent deployment, the 
airbag should be considered an essential system. Finally, the airbag 
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.
    In order to be an effective safety system, the airbag must function 
properly and must not introduce any additional hazards to occupants as 
a result of its functioning. There are several areas where the airbag 
differs from traditional occupant protection systems, and requires 
special conditions to ensure adequate performance.
    Because the airbag 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 
airbag. Since an actual crash is frequently composed of a series of 
impacts, this could render the airbag 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 
protection proportional to the severity of the impact. Therefore, the 
airbag installation should be such that the airbag will provide 
protection when it is required, and will not expend its protection when 
it is not needed. There is no requirement for the airbag to provide 
protection for multiple impacts, where more than one impact would 
require protection.
    The airbag will also potentially serve more than one occupant 
although, since seats could be unoccupied, this may not always be the 
case. It will be necessary to show that the required protection is 
provided for each occupant regardless of the number of occupied seats.
    Since a seat could be occupied by a wide range of occupants, the 
airbag should be effective for a wide range of occupants. The FAA has 
historically considered the range from the 5th percentile female to the 
95th percentile male as the range of occupants that must be taken into 
account. 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, and so it would not be necessary to show that 
the airbag will enhance the brace position. However, the airbag must 
not introduce a hazard in that case by deploying into the seated, 
braced occupant.
    Since the airbag 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. A separation that 
occurs at the location of the airbag would not have to be considered.
    Since the airbag is likely to have a large volume displacement, the 
inflated bag could potentially impede egress of

[[Page 28317]]

passengers. Since the bag deflates to absorb energy, it is likely that 
an airbag would be deflated at the time that persons would be trying to 
leave their seats. Nonetheless, it is considered appropriate to specify 
a time interval after which the airbag may not impede rapid egress. Ten 
seconds has been chosen as a reasonable time since this corresponds to 
the maximum time allowed for an exit to be openable. In actuality, it 
is unlikely that an exit would be prepared this quickly in an accident 
severe enough to warrant deployment of the airbag, and the airbag will 
likely deflate much quicker than ten seconds. Since the Jetstream 4101 
does not have an airbag installed at an exit passageway, the case where 
the seats are unoccupied is not critical.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Jetstream must show that 
airbag-equipped 4100 series airplanes comply with the regulations in 
the U.S. type certification basis established for the Jetstream Model 
4101 airplane. The U.S. type certification basis for the Model 4101 is 
established in accordance with 14 CFR 21.29 and 21.17 and the type 
certification application date. The U.S. type certification basis is as 
follows:

--14 CFR part 25 dated February 1, 1965, as amended by Amendments 25-1 
through 25-66 (based on the BAe application date to CAA-UK for TC), and
--14 CFR part 25, Amendments 25-67, 25-68, 25-69, 25-70, and 25-71, and
--14 CFR part 25, Secs. 25.361, 25.729, 25.571(e)(2), 25.773(b)(2) and 
25.905(d), all as amended by Amendment 25-72, and
--14 CFR part 25, Sec. 25.1419 as amended by Amendments 25-1 through 
25-66 (BAe elected to comply with this requirement), and
--Special Conditions No. 25-ANM-48 issued August 29, 1991, Lightning 
and High Intensity Radiated Fields (HIRF), and
--Other special conditions
--FAA Exemptions as follows: Exemption No. 5587 issued January 13, 
1993, head impact criteria (25.562(c)(5)) for the three most forward 
passenger seats in the passenger cabin (Note: Exemption number 5587 is 
a time limited exemption that expires at the date specified therein 
unless extended by the FAA Transport Airplane Directorate.), and
--FAA Equivalent Safety Findings
--14 CFR part 34 effective September 10, 1990, and
--14 CFR part 36 effective December 1, 1969 as amended by Amendments 
36-1 through 36-18 including Appendices A, B and C.

    If the Administrator finds that the applicable airworthiness 
regulations (i.e., 14 CFR part 25 as amended) do not contain adequate 
or appropriate safety standards for Jetstream 4100 series airplanes 
because of a novel or unusual design feature, special conditions are 
prescribed under the provisions of 14 CFR 21.16 to establish a level of 
safety equivalent to that established in the regulations.
    In addition to the applicable airworthiness regulations and special 
conditions, the Jetstream Model 4100 must comply with the fire and 
exhaust emission requirements of 14 CFR part 34 and the noise 
certification requirements of 14 CFR part 36.
    Special conditions, as appropriate, are issued in accordance with 
14 CFR 11.49 after public notice, as required by 14 CFR 11.28 and 
11.29(b), and become part of the type certification basis in accordance 
with 14 CFR 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 novel or 
unusual design feature, or should any other model already included on 
the same type certificate be modified to incorporate the same novel or 
unusual design feature, the special conditions would also apply to the 
other model under the provisions of Sec. 21.101(a)(1).

Novel or Unusual Design Features

    The Jetstream Model 4100 series airplanes will incorporate the 
following novel or unusual features:
    The Jetstream Model 4100 series airplanes will utilize airbags to 
provide head injury protection for occupants seated behind interior 
walls and furnishings. The airbags will be activated by acceleration 
sensors that integrate the acceleration time history to determine 
whether the bag should be deployed. Inflation of the bag is 
accomplished by firing of a small pyrotechnic device.
    The FAR state the performance criteria for head injury protection 
in objective terms, and contain more specific criteria for systems and 
equipment. None of these criteria are adequate, however, to address the 
specific issues raised by airbags. The FAA has therefore determined 
that, in addition to the requirements of 14 CFR part 25, special 
conditions are needed to address requirements particular to an airbag 
installation.
    From the standpoint of a passenger safety system, the airbag is 
unique in that it is both an active and entirely autonomous device. 
While the automotive industry has good experience with airbags, the 
conditions of use and reliance on the airbag 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 activation system.
    The following proposed 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 airbags is a relatively rare event, and because the consequences 
of an inadvertent activation are potentially quite severe, these latter 
requirements are probably the more rigorous from a design standpoint.
    Accordingly, in addition to the requirements of 14 CFR 25.562 and 
25.785, these special conditions are issued for the Jetstream 4101 
airplane with a passenger airbag installation. Other conditions may be 
developed as needed based on further FAA review and discussions with 
the manufacturer and the Civil Aviation Authority (CAA).

Discussion of Comments

    Notice of Proposed Special Conditions No. SC-91-4-NM for the 
Jetstream Aircraft Ltd. Model 4101 airplane was published in the 
Federal Register on October 15, 1996 (61 FR 53680). Comments were 
received from two labor organizations and Jetstream Aircraft Ltd. Both 
labor organizations support the issuance of the special conditions, but 
request that the FAA consider the use of upper torso restraint system 
in conjunction with the airbag. One of the commenters contends that 
upper torso restraints are not impractical, as implied in the Notice. 
While the use of upper torso restraints for passenger seats is not a 
trivial design problem, the FAA agrees that it can be practical, and 
is, in fact, in use for one manufacturer. Nonetheless, the standards in 
the regulation are objective, and compliance with these special 
conditions will neither mandate nor

[[Page 28318]]

preclude the use of upper torso restraints. The FAA cannot insist on a 
particular means of compliance. In this case, Jetstream has elected to 
show compliance with the requirements through the use of airbags, and 
these special conditions are promulgated to establish the appropriate 
certification criteria for airbags. Thus, the issue of whether upper 
torso restraints should be required is outside the scope of these 
special conditions.
    Jetstream has commented that the requirement to accommodate 
occupants seated in the brace position should only apply to designs 
that have no deactivation feature. They contend that, in the case where 
a passenger would assume the brace position, there will be time to 
disable the airbag (since it wouldn't be needed for a person in the 
brace position), and therefore the requirement is not necessary for the 
Jetstream Model 4100. The FAA disagrees that the need to address the 
brace position is mitigated if the system has a deactivation 
capability. The possibility that a passenger will or will not be in the 
brace position cannot be disregarded, since the accident scenarios are 
unknown. The potential for a person to assume the brace position 
unnecessarily, as well as the potential for a person to fail to assume 
the brace position when necessary, must be considered. Therefore, the 
fact that the Jetstream system has a means to deactivate the system has 
no bearing on the proposed requirement. The requirement is adopted as 
proposed.

Applicability

    As discussed above, these special conditions are applicable to the 
Jetstream Model 4100. Should Jetstream apply at a later date for a 
supplemental type certificate to modify any other model included on 
Type Certificate No. A41NM to incorporate the same novel or unusual 
design feature, the special conditions would apply to that model as 
well under the provisions of 14 CFR 21.101(a)(1).

Conclusion

    This action affects only certain novel or unusual design features 
on one model of airplanes. It is not a rule of general applicability, 
and it affects only the manufacturer who applied to the FAA for 
approval of these features on the airplane.

List of Subjects in 14 CFR Part 25

    Air transportation, Aircraft, Aviation safety, Safety.

    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 delegates to be by the 
Administrator, the following special conditions are issued as part of 
the type certification basis for the Jetstream Aircraft Limited, 
Jetstream Model 4100 Series Airplanes:
    1. It must be shown that inadvertent deployment of the airbag, 
during the most critical part of the flight, will either not cause a 
hazard to the airplane or is extremely improbable.
    2. It must be shown that an inadvertent deployment that could cause 
injury to a standing or sitting person, is improbable.
    3. For the purposes of complying with Special Conditions No. 25-
ANM-48, high intensity radiated fields (HIRF), the airbag system is 
considered a ``critical system'' if its deployment could have a 
hazardous effect on the airplane; otherwise it is considered an 
``essential'' system.
    4. It must be shown that the airbag system is not susceptible to 
inadvertent deployment as a result of wear and tear or inertial loads 
resulting from inflight or ground maneuvers (including gusts and hard 
landings) likely to be experienced in service.
    5. It must be shown that the airbag will deploy and provide 
protection under crash conditions where its use is necessary to prevent 
serious head injury.
    6. It must be shown that the airbag will not be a hazard to 
occupants that are in the brace position when it deploys.
    7. The airbag must provide adequate protection for each occupant 
regardless of the number of occupants of the seat assembly.
    8. It must be shown that the airbag will not impede rapid egress of 
occupants after 10 seconds following its deployment.
    9. It must be shown that the airbag will not release hazardous 
quantities of gas or particulate matter into the cabin.
    10. The airbag must function properly after loss of normal 
electrical power, and after a transverse separation of the fuselage at 
the most critical location.
    11. The airbag installation must be protected from the effects of 
fire such that no hazard to occupants will result.
    12. There must be a means, that is operable by a crewmember, to 
verify the integrity of the airbag activation system.

    Issued in Renton, Washington, on May 14, 1997.
Stewart R. Miller,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service, ANM-100.
[FR Doc. 97-13588 Filed 5-22-97; 8:45 am]
BILLING CODE 4910-13-P