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FROM: THE BOEING COMPANY TO: Boeing Correspondence (MOM) [MESSAGE NUMBER:MOM - MOM - 15 - 0248 - 01B(R1)] Multi Operator Message MESSAGE DATE: 20 Apr 2015 1233 US PACIFIC TIME / 20 Apr 2015 1933 GMT CORRECTED COPY This message supersedes Message Number MOM - MOM - 15 - 0248 - 01B dated 19 -Apr- 2015 04:03:24 PM US PACIFIC TIME. Please destroy all copies of Message Number MOM - MOM - 15 - 0248 -01B. Reason for Corrected Copy: Clarification was include d to add ASG to the condition summary and to state that the Main and APU batteries do not need to be disconnected. Minor editorial corrections made. FROM: THE BOEING COMPANY TO: Boeing Correspondence (MOM) [MESSAGE NUMBER:MOM - MOM - 15 - 0248 - 01B] Multi O perator Message MESSAGE DATE: 19 Apr 2015 1602 US PACIFIC TIME / 19 Apr 2015 2302 GMT This message is sent to selected 787 - 8 and 787 - 9 Customers, Regional Directors, Regional Managers and Boeing Field Service Bases. CATEGORY: Maintenance, Engineering, Flight Operations, and Management. SERVICE REQUEST ID: 3 - 3222477079 ACCOUNT: Boeing Correspondence (MOM) DUE DATE: 22 -Apr- 2015 23:59 PRODUCT TYPE: Airplane PRODUCT LINE: 787 PRODUCT: 787 - 8/- 9 ATA: 2422 -02 SUBJECT: Action - GCU Clock Failsafe Preventative Maintenance REFERENCES: /A/ Power Deactivation AMM DMC - B787 -A- 24 - 22 -00 - 00Q- 510B -A

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - SUMMARY: This MOM is being sent to advise operators of an issue that could potentially interfere with normal operations of the 787. UTAS/Boeing recently confirmed a latent internal clock software2

issue where, if a GCU operates conti nuously without being powered down for approximately 248 days, it will enter a failsafe condition and the associated VFSG or ASG will go off- line. This message advises operators on methods to mitigate this issue until a GCU software update is available.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - DESCRIPTION: After a detailed software review and lab testing, UTAS and Boeing have determined that it is possible for an in - service 787 airplane which has not been powered down to a "Cold / Dark" state at some point during the last 8 months to experience a simultaneous failsafe of all six GCU positions. Please note that this condition has never occurred in - service. UTAS and Boeing believe that the probability is extremely low that a simult aneous failsafe of all six GCU positions will actually occur in the future because of relatively frequent airplane maintenance power down/power cycle activity. Also, please note that this condition is recoverable when the Generator Control Switches in the flight deck are cycled per existing QRH flight crew procedures. The FAA has indicated they intend to mandate action via an Immediately Adopted Rule Airworthiness Directive (AD). The following actions can be performed to prevent any potential operational im pacts and are anticipated to be sufficient to show compliance with the pending AD. DESIRED ACTION: ============== 1) Perform a Service Bulletin (SB) incorporation review on applicable 787s to determine if one or more of the following SB's has been complet ed with the last 120 days. These Service Bulletins require an airplane power cycle as part of incorporation. 787 - 24 - 0024 787 - 24 - 0039 787 -42 - 0006 787 -42 - 0009 787 -42 - 0010 787 -42 - 0013 787 -42 - 0014 2) For all 787's in - service which have not had at least one of the above listed SB's incorporated in the last 120 days, deactivate/remove all electrical power from the airplane, to a "Cold/Dark" state for at least 15 seconds per ref /A/, as soon as convenient. (The Main and APU batteries do not need to be disconnecte d.) 3) Develop a scheduled maintenance task for each 787 in - service to perform step 2) every 120 days until such a time that the planned GCU software update to resolve this issue is available and incorporated. Boeing requests each 787 operator perform a preliminary SB incorporation / airplane power deactivation assessment for each airplane and provide the date that the power cycle activity was performed to Boeing by 22 -Apr- 2015. The date of the power cycle will be documented by Boeing and communicated to the FAA.3

LONG TERM RESOLUTION PLAN: UTAS and Boeing are developing a GCU software upgrade that is anticipated to be released in Q4 2015. Boeing is also creating an FTD to describe / track this project and it will be published by the end of April 2015. Boeing also anticipates that this new GCU software SB will be mandated by AD after it is published. If attachments are referred to, and are not present, please access them by logging into MyBoeingFleet Service Requests application. If you have further qu estions, you may contact the appropriate Airline Support Manager. https://myboeingfleet.boeing.com/servicerequests/index.html?entityId=3 - 1H9PWSC&entityType=MultiOperatorMessage John Murphy - 787 Fleet Chief Courtney Makela Director - 787 Services Comme rcial Aviation Services The Boeing Company Corrected copy If attachments are referred to, and are not present, please access them by logging into MyBoeingFleet Service Requests application using the link below. If you have further questions, you may contact the appropriate Airline Support Manager. https://myboeingfleet.boeing.com/servicerequests/index.html?entityId=3 - 1HC3RRU&entityType=MultiOperatorMessage