Narrative:

At cruise; altitude prior to entering ETOPS; the left engine generator tripped off-line. This event caused the autopilot to disengage and manual control was immediately assumed. The APU was started and it picked up the load. Afterwards there was a noticeable thump; seeming to come from the left side of the aircraft. There were no adverse or noticeable engine fluctuations. This happened again several seconds later. There was no obvious explanation for this and it concerned us. Later flight attendants and passengers reported experiencing the same thumping. On a scale of one to ten; we agreed that it was a six. This was discussed with our mechanic on the ground. Upon autopilot disengagement I reselected the center autopilot it did not engage. I then selected the left autopilot and it successfully engaged. The QRH was called for and generator off checklist was run. Left generator reset was attempted once; as per procedure; and was unsuccessful. The generator off checklist was completed and we prepared for landing. When the auto brakes were selected the switch did not latch and went to disarm (two attempts) with the associated EICAS message. Shortly after that the antiskid EICAS message also appeared; causing us to consider a landing distance penalty. The status message showed altn antiskid and norm antiskid. Applicable QRH checklists were run. In addition the left center fuel pump was shed and cross-feed valve was opened in order to maintain fuel balance. Loss of right center fuel pump would have made center tank fuel unusable causing further ETOPS concern. ATC was contacted and advised that we needed to return. Company was called on satcom and advised. We selected the closest option until we received guidance from the company. Descent clearance was issued and in-range checklist was run. Based on the growing list of concerns; our judgment; and lack of timely guidance from the company; we committed to landing at one of two nearby airports depending on best runway length options and availability of ILS guidance. Weather conditions were light rain and gusty winds with MVFR conditions; but the winds settled down to approximately 12 KTS right down the runway at the closest airport. The final decision was made to land there. At some point during the descent the company asked us to divert to another further airport; but we felt this was unacceptable sighting all of the above factors; especially the two noticeable; undetermined thumps. The purser was advised of the situation and an announcement was made to the passengers. Based on all of our concerns including a wet surface; no antiskid; and overweight landing; it was decided that we should declare an emergency to be conservative. We received some delaying vectors while we determined performance numbers for anti skid inoperative and suitable airport and runway. The landing was smooth and the aircraft was stopped in a relatively short distance with minimal brake heating. No assistance was required and we taxied to parking slowly to cool brakes. Logbook entries were entered and maintenance was consulted; discussing all factors. Crew coordination was exemplary and all crew members followed procedure well; demonstrating a high degree of proficiency; knowledge; and judgment.

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Original NASA ASRS Text

Title: An ETOPS B757-200 charter flight diverted to a nearby airport prior to entering ETOPS due to the loss of the Left Engine Generator and subsequent failures of associated systems. An unexplained 'thumping' sound from the left side of the aircraft contributed to the decision to divert at once despite the need for an overweight landing.

Narrative: At cruise; altitude prior to entering ETOPS; the left engine generator tripped off-line. This event caused the autopilot to disengage and manual control was immediately assumed. The APU was started and it picked up the load. Afterwards there was a noticeable thump; seeming to come from the left side of the aircraft. There were no adverse or noticeable engine fluctuations. This happened again several seconds later. There was no obvious explanation for this and it concerned us. Later Flight Attendants and passengers reported experiencing the same thumping. On a scale of one to ten; we agreed that it was a six. This was discussed with our mechanic on the ground. Upon autopilot disengagement I reselected the center autopilot It did not engage. I then selected the left autopilot and it successfully engaged. The QRH was called for and Generator Off checklist was run. Left generator reset was attempted once; as per procedure; and was unsuccessful. The Generator Off checklist was completed and we prepared for landing. When the auto brakes were selected the switch did not latch and went to disarm (two attempts) with the associated EICAS message. Shortly after that the ANTISKID EICAS message also appeared; causing us to consider a landing distance penalty. The status message showed ALTN ANTISKID and NORM ANTISKID. Applicable QRH checklists were run. In addition the left center fuel pump was shed and cross-feed valve was opened in order to maintain fuel balance. Loss of right center fuel pump would have made center tank fuel unusable causing further ETOPS concern. ATC was contacted and advised that we needed to return. Company was called on SATCOM and advised. We selected the closest option until we received guidance from the company. Descent clearance was issued and in-range checklist was run. Based on the growing list of concerns; our judgment; and lack of timely guidance from the company; we committed to landing at one of two nearby airports depending on best runway length options and availability of ILS guidance. Weather conditions were light rain and gusty winds with MVFR conditions; but the winds settled down to approximately 12 KTS right down the runway at the closest airport. The final decision was made to land there. At some point during the descent the company asked us to divert to another further airport; but we felt this was unacceptable sighting all of the above factors; especially the two noticeable; undetermined thumps. The Purser was advised of the situation and an announcement was made to the passengers. Based on all of our concerns including a wet surface; no antiskid; and overweight landing; it was decided that we should declare an emergency to be conservative. We received some delaying vectors while we determined performance numbers for anti skid inoperative and suitable airport and runway. The landing was smooth and the aircraft was stopped in a relatively short distance with minimal brake heating. No assistance was required and we taxied to parking slowly to cool brakes. Logbook entries were entered and maintenance was consulted; discussing all factors. Crew coordination was exemplary and all crew members followed procedure well; demonstrating a high degree of proficiency; knowledge; and judgment.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.