The National Transportation Safety Board (NTSB) has released its final report on Delta Air Lines Flight 211, which experienced an unusual autopilot error mid-way through its flight in July 2022.
Background
Although the flight number has since been reassigned to Delta's South Africa services, during 2022, DL211 was the return leg from Prague (PRG) to New York (JFK). The service took off from Prague at around 14:00 CEST for a relatively long 9-hour leg between the two cities with 221 passengers and 12 crew members onboard. DL211 was operated by one of Delta's older Boeing 767-300s, the 30-year-old N181DN.
Around halfway through the flight, as the aircraft was passing the southern edges of Greenland, cabin crew members reported flooding within the mid-cabin and forward-left lavatories.
While an out-of-service lavatory is rarely an emergency, as the flight progressed, the flight deck crew noticed that the autopilot had disconnected and that there were some issues with the aircraft's roll control. When the team attempted to rectify the situation, they became aware that they could not reconnect any of the aircraft's three autopilots or correct the aircraft's gradual right drift.
After contacting dispatch and flight maintenance, the crew declared an emergency and began diverting to Gander Airport (YQX), descending to 9,000 feet. As the jet descended through 12,000 ft, the crew felt a slight jolt through the aircraft, finding themselves now able to regain control of the flight. The emergency squawk was canceled, and though a stopover at Boston's Logan International Airport (BOS) was briefly considered, the aircraft had enough remaining fuel to make it back to New York, landing back at JFK at 17:46 EDT – an hour later than scheduled.
Upon landing at JFK, the aircraft was pulled from commercial flights for several days, heading off to Delta Air Line's TechOps at Atlanta's Hartsfield-Jackson International Airport (ATL) for some repairs.
According to the Transportation Safety Board of Canada (CTSB), the carrier inspected the autopilot and roll control, along with replacing the grey water drain masts for the toilets and a seal close to the aileron centering and trim mechanism. N181DN was given the green light to return to service on July 12.
NTSB findings
In its report published Friday, the NTSB unveiled an unusual sequence of events that linked the faulty toilets to the 767's limited flight controls and autopilot error.
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While it may be easy to lay the blame on a geriatric jet, July's incident appears to be one of simple human error. In the report, Delta Air Lines MRO noted that during corrective action, personnel discovered that the drain mast heater circuit breakers for the forward and aft toilets had been left open, likely during the aircraft's prior maintenance in June 2022. Delta Air Lines replaced the elements as a precaution and reported them functioning normally during subsequent testing.
The NTSB concluded,
“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.”
What are your thoughts on the NTSB report for Delta Air Lines flight 211? Let us know in the comments.
Source: The Aviation Herald