[Federal Register Volume 63, Number 214 (Thursday, November 5, 1998)]
[Rules and Regulations]
[Pages 59692-59695]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-29626]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM148; Special Conditions No. 25-141-SC]
Special Conditions: Boeing Model 777 Series Airplanes; Seats With
Articulating Seat Backs
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions.
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SUMMARY: These special conditions are issued for Boeing Model 777
series airplanes with articulating seat backs. The applicable
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 provided by the existing
airworthiness standards.
EFFECTIVE DATE: December 7, 1998.
FOR FURTHER INFORMATION CONTACT: Jeff Gardlin, Propulsion, Mechanical
Systems, and Crashworthiness Branch, ANM-112, Transport Airplane
Directorate, Aircraft Certification Service, FAA, 1601 Lind Avenue SW.,
Renton, Washington 98055-4056; telephone (206) 227-2136; facsimile
(425) 227-1149.
SUPPLEMENTARY INFORMATION:
Background
On April 15, 1998, the Boeing Company applied for a change to Type
Certificate No. T00001SE to include Model 777 series airplanes equipped
with seats with articulating seat backs (seats that have a portion of
the seat back that moves under inertia loads). Sicma Aero Seat, a
Boeing supplier, has designed a seat for installation on a Boeing 777-
300 airplane with an articulating seat back that is designed to rotate
forward under a prescribed inertial load. The prescribed inertial load
is slightly below the 16g test condition of Sec. 25.562. The inertial
load causes the seat back mounted video monitor and headrest assembly
to partially separate from the seat back and pivot forward. The goal of
the design is to reduce the mass of the upper seat back subject to
impact, thereby reducing the Head Injury Criteria (HIC) measurement and
enhancing passenger safety.
Section 25.562 specifies the dynamic test criteria 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. While the test conditions described in this section are
specific, it is the intent of the requirement that an adequate level of
head injury protection be provided for crash severities up to and
including that specified.
The FAA has established guidance, known as ``simplified HIC
certification,'' described in a February 1996 Transport Airplane
Directorate memorandum, which provides a simplified procedure for
demonstrating compliance with the HIC requirements of
Sec. 25.562(c)(5). This procedure provides test conditions that meet
the intent of the requirements, without causing excessive testing to be
performed. The typical seat back has three areas that are considered
head strike zones within the +/-10-degree yaw range of impact
orientation. The procedure describes two different tests that address
these three head strike zones for the majority of cases.
Because Sec. 25.562 and FAA guidance do not adequately address
seats with articulating seat backs, the FAA recognizes that appropriate
pass/fail criteria need to be developed that do 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 Model
777 airplanes equipped with seats with articulating seat backs comply
with the regulations in the U.S. type certification basis established
for the Model 777 airplane. The U.S. type certification basis for the
Model 777 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 listed in Type Certificate Data Sheet No. T00001SE.
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 Boeing Model 777 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 Boeing Model 777 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.
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 21.101(b)(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 Boeing Company has proposed installing seats with articulating
seat backs on a Boeing Model 777-300 airplane. The articulating seat
back is designed to rotate forward under a prescribed inertial load.
The prescribed inertial load is slightly below the 16g test condition
specified in Sec. 25.562. The inertial load causes the seat back
mounted video monitor and headrest
[[Page 59693]]
assembly to partially separate from the seat back and pivot forward.
The goal of the design is to reduce the mass of the upper seat back
subject to impact, thereby reducing the HIC and enhancing passenger
safety.
The Federal Aviation Regulations (FAR) state the performance
criteria for head injury protection in objective terms. Additionally,
as discussed earlier in this document, the FAA has established further
guidance to address head injury protection for the majority of cases.
However, none of these criteria are adequate to address the specific
issues raised concerning seats with articulating seat backs. 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 installation of seats with articulating seat backs.
Accordingly, in addition to the passenger injury criteria specified
in 14 CFR 25.562 and 25.785, Boeing must also comply with these special
conditions for Model 777 series airplanes equipped with seats with
articulating seat backs. Note that HIC, which is addressed in this
special condition, does not address occupant injury due to contact with
sharp edges or protrusions. Damage to the anthropomorphic test device
(ATD) may be used as part of the evaluation of protrusions and sharp
edges in demonstrating compliance with Sec. 25.785(b). Other conditions
may be developed, as needed, based on further FAA review and
discussions with the manufacturer and civil aviation authorities.
Discussion
The seat with the articulating seat back is a new and complex
design that warrants additional requirements to ensure an equivalent
level of safety to that provided by the regulations. This seat reduces
the effective mass that an occupant contacts during a high inertial
load, thereby increasing the amount of head injury protection. However,
additional considerations are necessary to ensure that the articulating
seat back design does not introduce other hazards to occupants. If the
articulating seat back fails to break away at the designed inertial
load, the seat back may remain rigid, resulting in a significantly
higher head injury than allowed for in the regulations. To ensure that
the occupant does not contact a rigid seat back, the seat back must
break away each time the designed break away inertial load is
encountered.
In addition, it is important to evaluate the articulating seat back
at lower values than the designed break away inertial load. During a
lower inertial load, the occupant may also contact the seat. Since the
seat will not break away prior to the occupant contacting the seat
during this lower inertial load, the occupant may receive a more severe
head injury than during an event occurring at the designed break away
inertial load. The intent of the regulations is that the occupant is
protected from head injury for crash severities up to and including
that specified.
When the articulating seat back breaks away, the video monitor
pivots and moves forward, leaving a rectangular opening in the seat
back. This opening could pose an entrapment hazard to the person seated
behind the seat. During any testing for certification, the head must
not become entrapped. In addition, the head must not become entrapped
in any other foreseeable operating conditions for the range of
occupants.
The articulating seat back may have protrusions and/or recessed
areas (i.e., bottom lip of the seat back opening) that pose a head
injury hazard to the occupant during emergency conditions. As stated in
Sec. 25.562(c)(5), the head impact for a seat occupant cannot exceed a
HIC of 1,000 units. The ``simplified HIC certification'' procedure is
commonly used to demonstrate compliance with Sec. 25.562(c)(5). Due to
the non-standard articulating seat back configuration, the ``simplified
HIC certification'' procedure alone may not be sufficient for
demonstrating compliance with Sec. 25.562(c)(5). The ATD must come in
contact with these protrusions or recessed areas of the seat back
opening during testing. If the ATD does not contact these areas using
the ``simplified HIC certification'' procedure, additional testing will
be required to demonstrate compliance with Sec. 25.562(c)(5).
Discussion of Comments
Notice of Proposed Special Conditions No. 25-98-03-SC for Model 777
series airplanes equipped with articulating seat backs was published in
the Federal Register on June 4, 1998 (63 FR 30423). Six commenters
responded.
One commenter had no objection to the special conditions. Two of
the commenters generally agreed with the need for special conditions,
but requested clarifications regarding certain of the specific
conditions. The remaining three commenters did not agree that special
conditions were warranted.
Several commenters requested a more specific definition regarding
the level of reliability intended by the special conditions. Commenters
contend that, while a reliable system is desirable, the level of
reliability should be made clear. The FAA agrees that the term
``reliable'' is open to interpretation and should be clarified. In this
context, the FAA intends that the system be demonstrated to perform as
reliably as other means of head injury protection. This will require
testing to establish that the design results in repeatable performance.
The FAA considers that 18 successful tests, without failure, would
constitute acceptable performance. The FAA notes that this will require
only three dynamic tests, since 6 seatbacks can be tested at once.
Other commenters discuss the requirement that the HIC be shown to
be less than 1000 for other impact conditions, where the seatback does
not break away. Some commenters believe that the wording of the special
conditions implies multiple tests at various conditions. The intent of
this condition is to ensure that the articulating feature will activate
at the minimum impact level that could produce 1000 HIC. Therefore, a
test at the maximum impact at which the seatback does not deploy that
results in a HIC of less than 1000 would be sufficient. The FAA agrees
that the wording of this requirement is not entirely clear, and it has
been changed accordingly.
Another comment concerned the discussion in the preamble regarding
lacerations and damage to the ATD. The commenters do not agree that the
ATD is an acceptable vehicle for making such assessments, and question
whether lacerations qualify as ``serious'' injuries. This discussion is
not part of the special conditions themselves, but rather an
informational aside concerning the utility of the HIC measurement. The
FAA is aware that the ATD will not behave in the same manner as a human
being with respect to laceration and will take this into account. In
this regard, this seat is not considered particularly different than
other seats, and therefore no special condition on this matter is
proposed. The issue has been adequately addressed on other designs up
to now.
The issue of head entrapment was also the subject of several
comments, especially concerning the language ``under any other
foreseeable operating or crash conditions.'' The intent of this
requirement is to ensure that the opening created in the seatback does
not have the potential to entrap an occupant's head, even if the
entrapment does not happen to occur during the specific dynamic tests
conducted to demonstrate compliance with other
[[Page 59694]]
requirements. That is, just because the head of the ATD might not
become entrapped does not necessarily indicate that entrapment is not
an issue. Nonetheless, the FAA agrees that considering the phrase ``any
other foreseeable crash condition'' literally would require an
excessive amount of tests. The severity of the impact is considered
limited by the requirements of Sec. 25.562. It is the potential for
entrapment that might be variable, depending on occupant size, or
precise angle of impact. The FAA has determined that these variables
can be assessed using the dynamic tests that are conducted as a source
of baseline data.
Another commenter requested quantification of the term
``entrapment,'' and correlation between the energy needed to entrap the
head of the ATD, versus what would be required to entrap the head of a
person. In this regard, the FAA considers that entrapment of the ATD's
head is sufficient to indicate that a person's head would also be
entrapped. The remaining conditions, where the ATD's head is not
entrapped, but a person's head would be, are difficult to quantify. The
FAA does not have quantitative criteria available to make this
assessment in advance, but will review the data that are generated.
Considering that smaller occupants will not impact the seatback as high
as would larger occupants, it may be that the test with the ATD
impacting the opening will be sufficient to show compliance. The
wording of the special conditions has been modified to reflect the
discussion above.
One commenter notes that the HIC evaluation of a precise impact
target (the lip or edge of the opening) specified in the special
conditions will be difficult to achieve, due to the variability in such
tests. The FAA recognizes that there is difficulty in testing with a
precise target, but this should be a test objective. The FAA will
consider the results of the tests in conjunction with other data
supplied by the applicant to determine compliance with this requirement
if a direct assessment proves impractical.
Three commenters generally disagree with the special conditions and
contend that either the conditions are not justified, or that the
existing rules already address them.
One commenter believes that reliability should not be a requirement
of the special condition and is not contained within the dynamic test
performance standard. Other commenters agree that reliability is an
issue, but contend that the existing regulations already require it by
virtue of Sec. 25.601, which prohibits use of features that have been
shown to be unreliable. The FAA agrees that the dynamic performance
standards do not explicitly address reliability. Section 25.601 has not
been applied in this manner, and since the features employed here are
novel, the feature's reliability has not been demonstrated or
determined. Typically in type certification, the assumption is that the
type design is represented during certification testing and that all
such articles incorporating that type design will perform identically.
In this case, the dynamic performance of a feature intended to provide
injury protection might be demonstrated only one time. In making this
provision a part of the special conditions, the FAA has determined that
a single certification test is not adequate to show compliance.
These commenters also question the need to address HIC when the
seatback does not break away. They contend that the conditions as
described are too numerous to address, or that the potential for injury
in this case is too low to consider. Regarding the former issue, the
special condition has been clarified as noted above. Regarding the
latter issue, the FAA would be willing to consider the question of
whether the potential for HIC greater than 1000 was negligible when the
seatback does not break away, if there are credible data to support
that conclusion. Nonetheless, the issue needs to be addressed, whether
or not additional tests result.
These commenters also questioned the issue of entrapment of the
head as already addressed by the regulations. Owing to the particular
design, the issue of entrapment is not considered to the extent
necessary by the current regulations. As discussed above, the
performance of the ATD in a particular test may not be indicative of
the situation in general. In this case, the design tends to create a
potential area for head entrapment as part of its intended operation.
This must be addressed explicitly.
Commenters question whether the issue of HIC on the seatback
opening is a requirement at all. These commenters contend that if no
contact with the opening occurs during a certification test, then it is
not required to be substantiated directly. The commenters cite previous
FAA guidance concerning establishment of head strike envelopes and
simplified test methods. The FAA notes that the methods cited are
dependent on more or less homogeneous contact surfaces that are not
sensitive to minor variation in head path. The articulating seatback
creates a discontinuity in the impact surface that can only be
addressed directly. That is, if the discontinuous area is within the
headstrike envelope it does not fall under the guidance previously
issued. As noted above, the FAA recognizes the difficulty in trying to
assess a specific target, but this must be the objective.
Comments related to the consideration of sharp edges parallel those
discussed earlier, and again, are not part of the special conditions
themselves.
Many commenters also noted that proposed Special Condition 5 is
essentially a restatement of Sec. 25.562(c)(8). After further
consideration, the FAA agrees that this special condition is redundant,
and it is therefore withdrawn.
Except as noted above, the special conditions for the Model 777
series airplanes equipped with articulating seat backs are adopted as
proposed.
Applicability
As discussed above, these special conditions are applicable to the
Model 777 series airplanes. Should Boeing apply at a later date for a
change to the type certificate to include another model incorporating
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 the Boeing Model 777 series 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 delegated to me by the
Administrator, the following special conditions are issued as part of
the type certification basis for Boeing Model 777 series airplanes
equipped with seats with articulating seat backs:
1. The articulating seat back must reliably break away at the
designed inertial load.
2. The HIC value must not exceed 1,000 units under the maximum
inertia loading conditions under which the articulating seat back will
not break away.
[[Page 59695]]
3. The head must not become entrapped in the seat back opening
created by the articulating seat back, during any testing conducted to
demonstrate compliance with Secs. 25.562 and 25.785(b), and these
special conditions. The head must also not become entrapped in the seat
back opening during any other foreseeable operating conditions.
4. The HIC must not exceed 1,000 units for any obvious protrusions
or recessed areas of the seat back opening (i.e., bottom lip of the
seat back opening). The anthropomorphic test device (ATD) must come in
contact with these protrusions or recessed areas of the seat back
opening.
Issued in Renton, Washington, on October 23, 1998.
John J. Hickey,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 98-29626 Filed 11-4-98; 8:45 am]
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