[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]
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