[Federal Register Volume 65, Number 145 (Thursday, July 27, 2000)]
[Notices]
[Pages 46194-46195]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-18994]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration


Guidance for Demonstrating Compliance With Seat Dynamic Testing 
for Plinths and Pallets

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION:  Notice of additional clarification on an acceptable means of 
compliance.

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SUMMARY: This notice provides additional clarification on an acceptable 
means for demonstrating compliance with the airworthiness standards for 
seats installed on ``plinths'' and ``pallets'' of transport category 
airplanes. It is necessary to give the public guidance in this area and 
is intended to further explain the guidance contained in AC 25.562-1A 
and promote greater standardization and equal treatment among 
applicants.

FOR FURTHER INFORMATION CONTACT: Federal Aviation Administration, 
Attention: Jeff Gardlin, Airframe/Cabin Safety Branch, ANM-115, 
Transport Airplane Directorate, Aircraft Certification Service, 1601 
Lind Avenue SW., Renton WA 98055-4056; telephone (425) 227-2136, 
facsimile (425 227-1320.

SUPPLEMENTARY INFORMATION: The information contained in this notice was 
taken directly from FAA Memorandum No. 00-115-3, dated February 22, 
2000.

    ``The purpose of this memorandum is to provide additional 
clarification on acceptable means to demonstrate compliance with 
Sec. 25.562, of the FAR [Federal Aviation Regulations] for seats 
installed on ''plinths'' and ``pallets.'' Abbreviated criteria for 
testing plinths and pallets are given in paragraph 10.e., of 
Advisory Circular (AC) 25.562-1A [Dynamic Evaluation of Seat 
Restraint

[[Page 46195]]

Systems & Occupant Protection on Transport Airplanes].
    ``The issue of plinths versus pallets was raised in the Aviation 
Rulemaking Advisory Committee seat test harmonization working group 
that helped develop the revised AC and was considered, at the time, 
to be of relatively minor importance. Thus, a simple procedure was 
included in lieu of a detailed discussion of the underlying 
rationale for the criteria in the AC. However it now appears that 
the frequency of plinth and pallet installations is increasing, and 
the simple criteria in the AC are not always sufficient to address 
the design variations that are being presented for certification. 
This memorandum is intended to provide further explanation of the 
guidance contained in the AC and promote greater standardization and 
equal treatment among applicants.
    ``In order to clarify the appropriate certification procedures 
for plinths and pallets, a brief review of the regulation is needed. 
Section 25.562(b)(2) requires that the seat be subjected to a 
prescribed 16g dynamic impulse, with the points of attachment (floor 
rails or fitting) misaligned with respect to each other. The 
misalignment is intended to address local distortion between the 
seat and airplane floor. A lack of tolerance to local distortion has 
been a primary cause of seat attachment failures, and a fundamental 
object of the regulation is to provide for improved retention of 
seats. Based on accident and research data, the interface between 
the seat and airplane has been identified as critical and the 
regulation requires that interface to be tested to the prescribed 
16g dynamic impulse. The basic airplane follow structure beyond the 
interface (beams, intercostal etc.) is not required to be 
dynamically tested or demonstrated to tolerate misalignment. In the 
case of seats that do not attach directly to the airplane seat track 
(or equivalent), there is a need to establish the critical 
interface.
    ``The Advisory circular characterizes a plinth as an adapter 
used to attach a single seat to the floor, and gives an example of a 
pallet as an adapter used to attach multiple rows of seats. If the 
seat is essentially connected to the seat track via an adapter, the 
adapter is functionally part of the seat, and certification testing 
should take this into account. In that case, the seat and its 
adapter would be tested dynamically, with the misalignment required 
by the regulation imposed at the interface of the adapter and the 
floor.
    ``On the other hand, if seats were installed into the airplane 
with an adapter(s) such that the adapter(s) was effectively part of 
the airplane floor, then the critical interface would be between 
that seat and the adapter. In that case, the dynamic tests would 
include the seat and its attachment to the adapter, with the 
misalignment imposed on that interface.
    “In order to give a simple characterization of the two 
situations, the AC refers to single seats and multiple row seats. 
The term `single seat,', as used in the AC, was intended to refer to 
a seat assembly, which could be as large as five seat 
places.However, the rationale behind this characterization was that 
a single seat adapter would be considered a plinth, by virtue of its 
size and purpose, and therefore a part of the seat. Conversely, a 
multiple row seat installation was considered sufficiently large 
that the adapter would have to be a pallet, and therefore part of 
the floor.
    ``Nonetheless, using the rationale discussed above, there exists 
the potential for large plinths and small pallets. The issue is 
whether the critical interface is between the seat and the adapter, 
or between the adapter and the airplane. Generally speaking adapters 
of the size that contain a single row of seats (whether they are 
individual seat places or a common assembly) and mount into seat 
tracks, should be treated as part of the seat for purposes of 
certification in accordance with Sec. 25.562. Larger, or more 
integrally mounted, adapters should be assessed to determine whether 
they should be treated as part of the floor for purposes of 
certification in accordance with Sec. 25.561.''

    Issued in Renton, Washington on July 14, 2000.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service, ANM-100.
[FR Doc. 00-18994 Filed 7-26-00; 8:45 am]
BILLING CODE 4910-13-M