Daily Rules, Proposed Rules, and Notices of the Federal Government
Investigations of some recent aircraft accidents disclosed that ELTs mounted with hook and loop fasteners became dislodged from their mounting trays on impact. The separation of those ELTs from their mounting trays caused their antenna connection to sever, thus rendering the ELTs to be ineffective and unable to perform their intended function.
The FAA Modernization and Reform Act of 2012 (Pub. L. 112-95), Section 347(b)(1), required the FAA to determine if the ELT mounting requirements and retention tests specified by TSO-C91a and TSO-C126 were adequate to assess retention capabilities in ELT designs. Based on the determination, the Act, in Section 347(b)(2), required the Administrator to make any necessary revisions to the requirements and retention test to ensure ELTs remained properly retained in the event of an aircraft accident.
The FAA evaluated the mounting requirements and retention tests specified in TSO-C91a, TSO-C126, and TSO-C126a. After this evaluation, the FAA determined these standards did not adequately address the use of hook and loop fasteners. Hook and loop fasteners were not an acceptable means of compliance to meet the mounting and retention requirements of the ELT TSOs. While the evaluation of installation approval using hook and loop fasteners may meet the TSO requirements for retention forces in laboratory conditions, accident investigations found these fasteners did not perform their intended function.
The agency identified the following concerns after completing its evaluation of the use of hook and loop fasteners:
(1) Hook and loop fasteners fail to retain the ELT when insufficient tension is applied to close the fastener. There is no repeatable method for installation and no method to evaluate the tension of the hook and loop fastener. The allowance for pilots to secure ELTs to the aircraft when changing ELT batteries
(2) Hook and loop fasteners closed with proper tension may stretch or loosen over time due to wear, fluids, vibration, and repeated use, leading to insufficient tension to retain the ELT;
(3) Hook and loop fasteners closed with proper tension do not provide stated retention capability due to debris which can contaminate the hooks and loops of the fastener; and
(4) Hook and loop fasteners closed with proper tension degrade due to environmental factors such as repeated heating and cooling cycles, temperature extremes, and contamination resulting from location in equipment areas.
After publishing our initial intent to withdraw the TSO Authorizations (TSOA) for TSO-C91a, and TSO-C126/126a (See 135 FR 41,473 (2012)), the FAA considered five courses of action to mitigate safety concerns with the use of hook and loop fasteners to retain ELTs. These actions addressed design, production, and airworthiness approvals for both the TSO and retrofit for existing installations. Below is a summary of the actions and their outcomes:
The FAA issued an SAIB providing ELT installation and maintenance guidance and revised TSO-C126a to eliminate hook and loop fasteners from future TSO designs. The FAA is not issuing an airworthiness directive or a policy disallowing installation approval of ELTs that use hook and loop fasteners. Lastly, the FAA decided not to take the action of withdrawing the TSO authorizations of ELTs utilizing hook and loop fasteners as a mounting mechanism, but ask those aircraft owners/operators with ELTs secured with hook and loop fasteners in their aircraft to voluntarily switch to a metal strap type restraint method. Therefore, the proposed June 30, 2014 date for TSOA withdrawals is no longer applicable.