FAA mandate of design change
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The Icelandic Transportation Safety Board (ITSB) recommends to the FAA, to research the need for making inspections, and possible replacement, of spoiler actuator’s Blocking and Thermal Relief Valve Housing mandatory via issue of airworthiness directive, for Boeing 757 airplanes.
The FAA has issued Safety Recommendation 15.115, a Boeing 757 airplane level safety issue, mandating evaluation of the spoiler actuator's blocking and thermal relief valve housing failure to determine appropriate corrective action.
The FAA has reviewed and determined that the latent failure of the spoiler power control unit Blocking and Thermal Relief Valve (BTRV) housing does manifest itself when the hydraulic system it is attached to fails. The failure causes an uncommanded extension of the spoiler panel, known as spoiler panel float. The result of multiple spoiler panel floating can lead to the loss of the airplane. The FAA's Aircraft Certification Service has determined this is a safety issue and the FAA is in the process of publishing an airworthiness directive to address it.
The FAA has issued Airworthiness Directive 2017-04-07, mandating that within 51 months after January 23 2017, for all Boeing 757-200, -200PF, -200CB, and -300 series airplanes, certificated in any category, each spoiler power control unit (PCU) must be replaced with a new or changed PCU at spoiler positions 2, 3, and 4 on the left wing, and spoiler positions 9, 10, and 11 on the right wing, in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 757-27A0154, dated July 22, 2016. This concludes the above safety recommendation issued by the Icelandic Transportation Safety Board on August 13th, 2015.