What was found
IAD/BDL - FLT 6212 - DURING CRUISE AT 0830 HOURS ON 4-3-98, AIRCRAFT MADE AN UNSCHEUDLED LANDING DUE TO NR 1 ADC AND NR 1 AHRS FAILED. AIRCRAFT RETURNED TO GATE WITH NO FURTHER PROBLEMS. MAINTENANCE INSPECTED AND REMOVED AND REPLACED NR 1 ADC. OPS CHECK OK. AIRCRAFT WAS RELEASED AND APPROVED FOR RETURN TO SERVICE. REF: OPERATOR CONTROL NR VTZA98152.