What was found
FLT 3859 - EXPERIENCED A TORQUE FLUCTUATION OF THE NR 1 ENGINE AND INCREASE OF ITT TO APPROX 780 DEGREES. TORQUES DROPPED TO 50 PECENT FOLLOWED BY A LOUD GRINDING NOISE AND ENGINE FIRE INDICATION. INSPECTION VERIFIED NO INDICATION OF FIRE. ENGINE REMOVED AND REPLACED IAW DHC-8 MM. GROUND RUN AND OPERATIONAL CHECKS NORMAL. PRELIMINARY INVESTIGATION INDICATES APPARENT LP TURBINE BLADE SEPARATION. INVESTIGATION CONTINUES, AIRCRAFT RETURNED TO SERVICE. (M)