What was found
ON FINAL APPROACH TO HOSPITAL ROOF TOP HELIPORT, RPM WARNING HORN ACTIVATED FOLLOWED BY 15 TO 20 SECONDS OF POPPING AND GRINDING NOISES FROM NR 1 ENGINE. AFTER GAINING AIRSPEED, ENGINE WAS SECURED AND AN OEI LANDING WAS MADE AT BURBANK AIRPORT. SUBSTANTIAL DAMAGE TO NR 1 ENGINE INTERIOR WAS FOUND, CAUSE UNKNOWN AT THIS TIME. COMPLETE TWIN-PAC BEING SENT TO PRATT & WHITNEY FOR EVALUATION.