What was found
(CAN) AT 6,000 FEET IN CRUISE AT 80 PERCENT TORQUE, NR 2 ENGINE MADE A LOUD BANG WITH A GRINDING SOUND -'POOF SOUND'- THEN A CHIP DETECTOR LIGHT. THERE WAS NO PREVIOUS WARNING. PILOT REDUCED NR 2 ENGINE POWER TO IDLE AND LANDED ON A FROZEN LAKE. POST-FLIGHT INSP FOUND NO EXTERNAL DAMAGE OR OIL LEAKS. A BOLT HEAD (POSSIBLY A MS9488 OR MS9489) FOUND IN EXHAUST STACK. THE POWER TURBINE WHEEL WAS FOUND HEAVILY DAMAGED. FWD CHIP DETECTOR HAD SMALL AMOUNTS OF FERROUS METAL AND AFT CHIP DETECTOR WAS LOADED.