A Delta 767-300ER en route from Prague to New York on 7 July 2022 experienced a loss of aileron control as it neared the Canadian coast. After descending in preparation for an emergency landing in Canada, the pilots regained full control of the aircraft and were able to continue to New York. The NTSB this week issued their final report on the incident.
Pilots become plumbers
Two of the lavatories aboard the Delta 767 were leaking, one from an area near the toilet and the other from an area near the sink. The 767 was being operated by two complete crews, so the two pilots not flying investigated the leaks. After the leaks were noted, the water to those locations was shut off.
Soon after the leaks were reported, the first officer who was the pilot flying noted autopilot caution messages displayed on the EICAS. The aircraft was unable to make any lateral course changes. The autopilot was disconnected and the FO attempted to manually control the aircraft only to be able to make small adjustments on his control wheel.
The captain attempted similar inputs and was met with the same resistance by the aileron controls. The crew performed the “Jammed or Restricted Flight Controls” procedures and in coordination with Delta’s maintenance coordinators determined that ice formation due to the leaking lavatories was causing the control issues.
Declaring an emergency, the aircraft was instructed to descend to 9,000 feet where the air was above freezing. Passing through 12,000 feet the crew reported experiencing a minor jolt and the control wheel began operating normally.
The crew canceled their emergency and determined the aircraft had enough to fuel to land in New York flying at 11,000 feet.
NTSB report points to circuit breakers
The NTSB report says that the forward and aft lavatory drain mast heater circuit breakers were found open as Delta personnel performed an after flight inspection. Delta reported to the NTSB that the aircraft had undergone maintenance in June and returned to service on 23 June 2022. Flightradar24 data shows the 767 was out of service from 15 June to 23 June in Los Angeles before operating to Boston. Part of the maintenance actions performed by Delta during that period involved opening the forward and aft lavatory drain mast heater circuit breakers.
The NTSB reports the probable cause of the incident as “the failure of maintenance personnel to close the drain mast heater circuit breakers which resulted in the formation of ice in the forward drain mast, an improper flow of wastewater into the main landing gear wheel well, and the formation of ice on one or more aileron system components.”
