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

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of interim means of compliance.

SUMMARY:

This notice provides clarification of acceptable interim means for demonstrating compliance with the airworthiness standards for seats mounted on adapter plates of transport category airplanes. It is necessary to give the public guidance in this area and is intended to be used as a means of compliance until the FAA publishes superseding document(s).

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. 00-115-7, dated May 1, 2000.

“The purpose of this memorandum is to transmit acceptable interim means to demonstrate compliance with § 25.562 of the FAR [Federal Aviation Regulations] for seats installed on adapter plates, sometimes referred to as “plinths” or “pallets”.

“The attachment addressed a specific type of installation, for which the guidance contained in Advisory Circular (AC) 25.562-1A [Dynamic Evaluation of Seat Restraint Systems & Occupant Protection on Transport Airplanes], as clarified by Memorandum No. 00-115-3, may not provide sufficient information. Recent installations of multiple single-place seats into adapter plates, with the adapter plate installed into the airplane seat track (or other structure), have generated questions as to the proper certification procedure. In these cases, no dynamic testing incorporating the adapter plates was performed. The attached guidance addresses that issue.

“This guidance is interim, because additional data are needed to asses the interaction of seats/adapter plates/airframe. However, there are very near term projects where certification criteria are required before such data will be available. This guidance may be used until the FAA publishes a superseding document(s).

“Acceptable Interim Approach for Near Term Executive Interior Deliveries for Multiple Single Seats Mounted to an Adapter-Plate:

“Issue:

“Multiple single seats that are mounted to a single adapter-plate in the aircraft, are being tested to the 16g dynamic load conditions without the adapter-plate. The adapter-plate, which is attached to the aircraft seat tracks and, at times, to other attachment ‘hard points’, provides the load path to the aircraft structure. As a result of the adapter-plate not being incorporated in the test, it is unknown whether or not the seat-to-adapter-plate attachment, the adapter-plate itself, and the adapter-plate-to-aircraft-structure/seat track attachment are capable of reacting and distributing the seat loads into the aircraft structure.

“It is necessary to ensure that the seat remains attached to the aircraft floor structure under the prescribed 16g dynamic load condition. Failure in any of these load path details may result in a seat becoming detached from the aircraft floor structure. Therefore, the load path between the seat and aircraft floor structure must be shown to be capable of transferring the 16g seat dynamic loads.

“For the load path components between the seat leg attachments and the aircraft seat track or floor fittings, which were not represented/substantiated in the 16g dynamic seat test, a stress analysis of those details, using the peak loads recorded during the 16g dynamic tests, may be performed as an acceptable interim means of compliance to § 25.562(b) as provided below. Due to the limited amount of data available to assess the dynamic performance of this particular type of seating installation (seat/adapter-plate), this is interim action until such data are obtained to support policy addressing the subject installations. The FAA has identified that data from tests (to be performed possibly by CAMI) utilizing seats mounted on adapter-plates are needed to support long-term policy and guidance.

“Conditions necessary to use this interim approach are:

“—Each seat type (without adapter) has been dynamically tested in accordance with § 25.562, including pitch and roll.

“—The tested means of attachment is consistent with attachment of the seat to the adapter-plate.

“—Airplane floor warpage is addressed for the adapter-plate installation by providing an adequate number of distributed attachments of the adapter-plate to the airplane floor structure. The number of attachments will depend on the design of the adapter-plate and positioning of the seats on the plate. Typically the number of attachments will exceed the number of seat-to-adapter-plate attachments and shall not be less than the number of seat-to-adapter-plate attachments. The attachments of the adapter-to-aircraft structure must be structurally adequate to accommodate the dynamic loads and floor deformation.

“—Compliance with § 25.561 is achieved.

“If the actual attachment of the seat to the adapter-plate was not represented during the 16g dynamic seat test, it must be shown that the retention of the seat to the adapter-plate will not be compromised when the seat legs are subjected to the required pre-test pitch and roll conditions of § 25.562(b)(2). Testing of this condition may not be necessary if the attachment retention design and strength are shown to be capable of accommodating the dynamic loads and deformations.

“Analysis of load path components not tested:

“—Analysis of the seat-to-adapter-plate interface. It Must be shown that the seat/plate attachment is capable of reacting the measured peak 16g seat loads. The analysis must take into account eccentricities of load path and adapter-plate deformations that may induce prying (bending) loads at the attachment.

“—An analysis of the adapter-plate. It must be shown that the adapter-plate is capable of transferring the measured 16g peak loads from the seat-to-adapter-plate interface to the interface of the adapter-plate-to-aircraft floor structure (seat track lips and ‘hard points’).

“—Analysis of the adapter-plate-to-floor-structure interface. The aircraft seat track lips must be shown to be capable of reacting the measured peak 16g seat test load as distributed by the adapter-plate from the seats. The analysis must take into account eccentricities of load path and adapter-plate deformations that may induce prying (bending) loads at the attachment. In the case of hard point installations, the interface would be taken to the point at which the hard point interfaces with the aircraft floor structure (e.g., floor beam).

Note:

If a positive margin of safety cannot be achieved in the above analysis, either testing of the seat with the adapter-plate or redesign of the deficient interfaces will be required for compliance to § 25.562.

“If the actual seat/plate/aircraft-floor structure installation is planned to be tested, but the rigidity of the adapter-plate precludes the pre-test floor deformation condition from being performed, segments of the adapter-plate can be used for the interface between the seat and aircraft seat track section. This is in lieu of using the full plate. This will require however, that multiple attachments of the adapter-plate to the aircraft floor structure be provided. The intention of providing multiple distributed attachments is to indirectly address the potential deformation between the airplane floor structure and the plate. The number of attachments will depend on the design of the adapter-plate and positioning of the seats on the adapter-plate. The attachments of the adapter-plate-to-aircraft structure must be structurally adequate to accommodate the aircraft floor deformation.

“The FAA is also preparing a policy statement on the broader issue of compatibility of the seat installation with the airframe. This future policy statement will address this issue, and others, where they may be a question of the dynamic performance of the seat producing loads that exceed the structural capability of the airframe.”