What was found
FLIGHT CREW REPORTED MOMENTARY FAILURE OF NR 1 ENGINE (LOUD BANG, ROLLBACK OF ENGINE INDICATION, FOLLOWED BY ART FIRING, FOLLOWED BY ENGINE STABILIZATION UNTIL POWER REDUCTION FOR DESCENT THEN MORE ENGINE ROUGHNESS). MAINTENANCE PERSONNEL REMOVED AND REPLACED THE LEFT ENGINE IAW TASK CARD R0907101, OPS AND LEAK CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.