What was found
PDX FLIGHT: ON DESCENT THROUGH 11,000 FT, FA REPORTED PUNGENT 'BURNING TIRE' ODOR MOST EVIDENT BETWEEN ROWS 2 AND 5. THE CREW COULD SLIGHTLY DETECT AN ODOR ON THE FLIGHT DECK. NO CB'S POPPED AND ALL ENGINE INDICATIONS APPEAR NORMAL. MAINTENANCE FOUND THE ENGINES TO BE OVERSERVICED. DE-SERVICED TO APPROPRIATE LEVELS. BOROSCOPE NR 1 ENGINE. NO DEFECTS. GROUND RAN BLEEDS ON AT VARIOUS POWER SETTINGS FOR 20 MINUTES. NO BURNING TIRE ODOR NOTED. NO PARTS NOTED. AIRCRAFT RETURNED TO SERVICE.