What was found
SDP/ANC - FLT 1476 - AIRCRAFT EXPERIENCED A DUAL BLEED AIR FAILURE. TOTAL TIME OF FAILURE WAS APPROXIMATELY 10 SECONDS. THE FAILURES OCCURRED WHILE DESCENDING THROUGH 15,000 FEET IN CLEAR WEATHER AND MINUS 20 DEGREES CELSIUS OAT. CONDITIONS PRIOR TO THE FAILURES WERE AS FOLLOWS: ALTITUDE - FL210 FOR 2 HOURS IN CLEAR WEATHER AND MINUS 33 DEGREES CELSIUS OAT. MAINTENANCE COULD NOT FIND A REASON FOR THE FAILURES AND RETURNED THE AIRCRAFT TO SERVICE. (X)