What was found
DURING CLIMB, CADC LIGHT ILLUMINATED AND THE CAPTAIN`S AIRSPEED CLIMBED QUICKLY TOWARD THE BARBER POLE. SWITCHED TO ADC BOLT ON 2 AND CAPTAIN`S AIRSPEED RETURNED TO NORMAL. AFTER A FEW MINUTES, AND LATER WITH SEVERAL OVERSPEED WARNINGS AT 280KTS. EMERGENCY DECLARED, FLIGHT LANDED WITHOUT FURTHER INCIDENT. THE AIRCRAFT WAS GROUNDED. MAINTENANCE REPLACED THE CAPTAIN`S PITOT TUBE AND PERFORMED SATISFACTORY OPERATIONAL CHECK IAW AMM 34-11-02.