Narrative:

Near top of climb; advised by flight attendant that a passenger had noticed some 'sparks' coming from the left engine. Shortly after; this was confirmed by another flight attendant. Declared emergency; returned to ZZZ with left engine at idle to an uneventful landing. Advised that there were no further visual abnormals. There were no abnormal engine indications in the cockpit. Inspected by ground crew after landing; no abnormals. Taxi to gate uneventful.

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Original NASA ASRS Text

Title: A B757'S CABIN CREW REPORTED SPARKS FROM AN ENG. AFTER CONFIRMATION; AN EMER WAS DECLARED AND THE ACFT RETURNED TO LAND WITH THE ENG AT IDLE.

Narrative: NEAR TOP OF CLB; ADVISED BY FLT ATTENDANT THAT A PAX HAD NOTICED SOME 'SPARKS' COMING FROM THE L ENG. SHORTLY AFTER; THIS WAS CONFIRMED BY ANOTHER FLT ATTENDANT. DECLARED EMER; RETURNED TO ZZZ WITH L ENG AT IDLE TO AN UNEVENTFUL LNDG. ADVISED THAT THERE WERE NO FURTHER VISUAL ABNORMALS. THERE WERE NO ABNORMAL ENG INDICATIONS IN THE COCKPIT. INSPECTED BY GND CREW AFTER LNDG; NO ABNORMALS. TAXI TO GATE UNEVENTFUL.

Data retrieved from NASA's ASRS site as of May 2009 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.