As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 6551 - IAD-CLE - DURING CRUISE, AIRCRAFT MADE AN UNSCHEDULED LANDING DUE TO BOTH TRANSPONDERS FAILED. AIRCRAFT RETURNED TO GATE WITH NO FURTHER PROBLEMS. MAINTENANCE INSPECTED AND REMOVED AND REPLACED CAD C-2 COUPLER ADAPTER, OPS CHECK OK. AIRCRAFT WAS RELEASED AND RETURNED TO SERVICE. (M)