What was found
BWI - FLT 2821 - ON CLIMB-OUT FROM BWI, THE HEADING COMPARATOR LIGHT ILLUMINATED. CAPTAINS AND FIRST OFFICERS COMPASS SYSTEM SPLIT 30 DEGREES APART AND REMAINED THAT WAY FOR 10 MINUTES. CAPTAINS ADVISED BWI THAT HE WAS RETURNING TO FIELD. JUST PRIOR TO LANDING, COMPASS SYSTEM RETURNED BACK TO NORMAL. FLIGHT LANDED WITHOUT FURTHER INCIDENT. NO EMERGENCY WAS DECLARED. MAINTENANCE REMOVED AND REPLACED THE NR 1 DIRECTIONAL GYRO. OPERATIONAL CHECK NORMAL. (M)