[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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