Frozen Drain Leads to Flight Control Issues
N181DN, a Boeing B767-332 aircraft operated by Delta Air Lines, was conducting flight DAL211 from Prague-Václav Havel Intl (LKPR), Czech Republic to New York-John F. Kennedy Intl (KJFK), NY. When in cruise flight at about 56°35' N, 038°48' W, the flight crew was alerted to a flooding issue in the mid-cabin lavatories, followed shortly after with information that the forward left lavatory was also flooding. A short time after the flooding issue was discovered, the autopilot disconnected. The flight crew attempted to connect all 3 autopilot systems, but none would remain connected. The aircraft began to drift direction to the right, and correction to the left could not be made. The flight crew contacted company dispatch and maintenance control and completed the quick reference handbook (QRH) for a jammed flight controls state. The flight crew declared an emergency with Canadian air traffic services (ATS), began a descent and coordinated with ATS for a diversion to Goose Bay (CYYR), NL. At about 100 nm east of CYYR, while at an altitude of 12 000 feet, the aircraft flight control function returned to normal operation. The flight crew terminated the emergency and coordinated a diversion to Boston-Logan Intl (KBOS), MA. While enroute to KBOS at 11 000 feet a recalculation of fuel determined that the flight could continue to KJFK, where a landing was made without further incident.
Maintenance personnel replaced both grey water drain masts, and replaced a seal in the left wheel well canted pressure deck above the aileron feel centering and trim mechanism. The entire roll control and related autopilot systems were inspected and repairs effected as required.