Document ID: chunk:federal_register_of_legislation:F2009L02773:body:0:p2
Version: federal_register_of_legislation:F2009L02773
Segment Type: other
Provision Reference: 
Character Range: 2980–5522

accumulated 9,400 flight cycles (FC) or less, replace the clevis before the valve has accumulated 10,000 FC.

                If, at the effective date of this AD, the bypass valve has accumulated more than 9,400 FC, replace the clevis within 550 flight hours (FH) after the effective date of this AD.

                If it is not possible to determine the flight cycles accumulated by the bypass valve, replace the clevis within 550 FH after the effective date of this AD.

                For Requirement 2:

                If, at the effective date of this AD, the downlock assist valve, P/N 53341-5, has accumulated 9,400 FC or less, replace the clevis before the valve has accumulated 10,000 FC.

                If, at the effective date of this AD, the downlock assist valve has accumulated more than 9,400 FC, replace the clevis within 550 FH after the effective date of this AD.

                If it is not possible to determine the FC accumulated by the downlock assist valve, replace the clevis within 550 FH after the effective date of this AD.

                For Requirement 3:

                Within 4,500 FH after the effective date of this AD; or

                Within 6000 FH after the accomplishment of Requirement 1 of this AD; or

                Within 6000 flight cycles after the accomplishment of Requirement 2 of this AD,

                whichever comes first.
             This Airworthiness Directive becomes effective on 30 July 2009.
Background:  Investigation into a landing gear retraction problem on a production test flight revealed that, during aircraft pressurization and depressurization cycles, the pressure floor in the main landing gear bay deflects to a small extent.  This causes relative misalignment between the AES bypass valve, the downlock assist valve and the summing lever which, in turn, can result in damage to and potential failure of the respective clevis attached to one or both of the valves.  Such a clevis failure could remain dormant and, in the subsequent event that use of the AES was required, full landing gear extension may not be achievable.
             This AD gives instructions to replace the clevis, with a new part, for both the bypass and the downlock assist valves. It also gives instructions to install new support brackets for both valves, in order to increase the stiffness of the installations and thus prevent future relative misalignment and potential clevis failure.

James Coyne
Delegate of the Civil Aviation Safety Authority

19 June 2009