Japan Airlines

After effective of the existing AD2007-15-10, Japan Airlines (JAL) has replaced all of the No. 2 and No. 3 windows with two fail-safe interlayer windows 65B27046-( ) and 65B27047-( ) to extend the repeat interval, and then introduced the repeat inspection at every C-check interval not to exceed 7500 flight hours (or 5 years, whichever occurs first) which specified in the accomplishment instructions of Boeing Alert Service Bulletin 747-56A2012, dated August 24, 2006. As a result of the repeat inspection, JAL believes that it is almost possible to detect and correct the moisture ingression into the window which can contribute to interlayer cracks before return to service flight. Therefore JAL note that these are no significant issue which could result in loss of the window. Then, although Boeing has issued Service Bulletin 747-56A2012, Revision 1, dated August 12, 2010, which specifies the installation of the new dual structural glass pane windows, JAL still has not yet decided to introduce the installation of new windows due to economic impact since the parts price of dual structural glass pane windows is almost the twice by existing single pane windows. Note that the price of new dual structural glass pane windows 141U4821/141U4822 from Boeing Spares now offer the price 11318.00 USD pre each window. Also JAL is still not aware of certain field experience such as MTBR or MTBF of new dual structural glass pane windows so that it will be difficult to know how durable and excellent than existing single pane window. Due to above concern JAL would like to add the “Exception to compliance times to New Requirement of the AD” to allow the replacement with new dual pane window “within 22,000 flight-hours after new (or zero flight hours) of single pane window 65B27046-() or 65B27047-() was installed” in addition to compliance time “within 6 years after the effective date of this AD”, provided that JAL (Operators) continue to ensure that there is no such damage ev