As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKING OFF FROM RWY 30, AT GEAR RETRACTION ALTITUDE, CA'S AHRS FAILED. CREW NOTIFIED ATC AND REQUESTED VECTORS BACK TO IAD. NO EMERGENCY WAS DECLARED AND THE AIRCRAFT LANDED ON R1 WITHOUT FURTHER INCIDENTS. MECHANICS HAVE BEEN DISPATCHED TO THE AIRCRAFT. REPLACED NR 1 AHRS OPS CHECKED GOOD. PERFORMED OPS CHECK OF EHSI OPS CHECKED GOOD.