What was found
AFTER APPROX 30 MINUTES IN CRUISE, RECEIVED AN AIRSPEED DISAGREEMENT BETWEEN NR 1 & 2 PFDS, WITH AN INDICATION OF 10 KNOTS OR GREATER. DETERMINED THE NR 2 PFD FAULTY AND COUPLED NR 2 PFD TO NR 1 ADC. AFTER DESCENT AT ABOUT FL 37,000 THE AUTOPILOT DISENGAGED. ATTEMPTED TO RESET IT, NOTICED EADI WITH A PITCH OF 5 DEGREE, INDICATION NOSE UP, AND AIRSPEED 210 KNOTS AND SLOWING. VSI INDICATING A 2000 FT RATE OF DESCENT AND THE ALTIMETER SHOWING ACFT IN A DESCENT. DECLARED AN EMERGENCY. NR 1 PFD APPEARED TO START WORKING CORRECTLY. SUSPECT MOISTURE FREEZING IN PITOT SYSTEM. PITOT SYSTEM DRAIN PROCEDURE WAS PERFORMED AND A SIGNIFICANT AMOUNT OF MOISTURE WAS REMOVED FROM THE LT PITOT SYSTEM. FURTHER CHECKS ARE TO BE COMPLETED.