What was found
BOS - FLT 6439 - AFTER DEPARTURE CREW LOST BOTH TRANSPONDERS, TCAS, AUTO-PILOT, YAW DAMPENERS, AND FLIGHT DIRECTORS. AIRCRAFT DIVERTED BACK TO BOSTON AND LANDED WITHOUT INCIDENT. MAINTENANCE FUOND THE AIR DATA COMPUTER (ADC) TO BE DEFECTIVE. THE ADC WAS REPLACED, REQUIRED OPERATIONAL CHECKS WERE PERFORMED AND THE AIRCRAFT RETURNED TO SERVICE. (M)