What was found
(CAN) CREW REPORTED TO MAINTENANCE THAT THE CAPTAINS AIRSPEED INDICATOR WAS READING UP TO 40 KNOTS LOWER THAN CO-PILOTS AIRSPEED IN FLIGHT. PITOT STATIC LEAK CHECK AND VISUAL INSPECTION OF AIRCRAFT REVEALED BOTH CAPTS PITOT AND STATIC PLASTIC LINES MELTED FROM CONTACTING COCKPIT UNDERFLOOR HEATER DUCT. PITOT AND STATIC PLASTIC LINES WERE ROUTED ADJACENT TO THE HEATER DUCT. THE PROBLEM WAS FOUND UNDER THE COCKPIT FLOOR.