What was found
PHL-HPN FLIGHT 3668 AT 13,000 FEET IN CRUISE FLIGHT NR 1 HYDRAULIC SYSTEM FAILED. ROLL SPOILER INBOARD HYDRAULIC AND NR 1 HYDRAULIC ISOLATION LIGHTS ILLUMINATED. EMERGENCY DECLARED AND FLIGHT DIVERTED TO ISP. HYDRAULIC QUANTITY AT .5 QUART UPON LANDING. NORMAL BRAKES WERE INOPERATIVE. EMERGENCY BRAKES WORKED NORMALLY. MAINTENANCE INSTALLED A 36 INCH LONG FLEXIBLE HYDRAULIC LINE. LEAK CHECK WAS GOOD IN ACCORDANCE WITH DEHAVILLAND DASH 8 MM 20-50-52. LEFT AND RIGHT HYDRAULIC SYSTEM SERVICED. SPOILER LINE LOCATED AT TOP CENTER FUSELAGE JUST AFT OF FORWARD WING SPAR. AIRCRAFT RETURNED TO SERVICE.