A Delta Air Lines flight bound for Boston from Barcelona turned around over the Atlantic Ocean on Sunday and made an emergency landing in Porto, Portugal, after smoke filled the cabin mid-flight. Four people, including three passengers and one crew member, were hospitalized, and the diverted Airbus A330 forced Delta to scramble replacement flights for the 296 people on board.
A Mid-Ocean Turnaround
Flight DL251 departed Barcelona at 3:15 p.m. local time Sunday and was roughly two and a half hours into its scheduled eight-and-a-half-hour journey to Boston when the crew reported a mechanical issue and smoke in the cabin, according to the New York Post. The jet had flown over La Rioja and Galicia in Spain and was about 500 miles off the Portuguese coastline, reaching a maximum altitude of roughly 32,000 feet, before the crew turned back. As it crossed the ocean, the flight crew broadcast the emergency transponder code “Squawk 7700” to international air traffic control, according to AIRLIVE, before landing safely on Runway 35 at Francisco Sá Carneiro Airport in Porto.
The aircraft involved was an 11-year-old Airbus A330-300 registered under tail number N824NW, which first entered service with Delta in June 2015, according to The Aviation Hub. That makes the jet younger than Delta's average A330-300, a sub-fleet of 31 aircraft with an average age of 17.7 years, per the same outlet's reporting.
Dozens Treated on the Tarmac
Twelve people required oxygen while still in the air, and eight were treated on the tarmac once the plane landed, according to the Post's reporting. Emergency management officials in Portugal triggered a Level 2 alert at the airport, deploying roughly 60 emergency responders and 22 emergency vehicles to meet the wide-body jet, per The Economic Times.
Two male passengers were admitted to the emergency department at São João Hospital in Porto after experiencing smoke inhalation, a facility identified in social media reporting cited in the dossier. A hospital spokesperson said the two men had mild respiratory symptoms and were in stable condition.
Cascading Cancellations
The stranded aircraft and its displaced crew forced Delta to cancel two subsequent scheduled transatlantic flights, DL276 and DL277, according to AIRLIVE's reporting. The other passengers were not put on an alternative Delta flight that evening, while the Boston-bound flight that had been due to depart Porto at 1 p.m. Monday was canceled, according to FlightAware data cited by the Post. Delta instead planned to operate a replacement Boston-bound flight out of Barcelona at 3:15 p.m. Monday.
Earlier in the year, a Delta flight experienced an engine failure in São Paulo in March. Separately, a Delta plane bound for Fort Lauderdale made an emergency landing back at Atlanta's Hartsfield-Jackson Airport in August after departing around 7 a.m. and returning within 15 minutes; an airline representative said at the time that the plane returned out of an abundance of caution.
Why Crews Turn Back for Smoke
Cabin smoke and fume events can prompt crews to divert to a suitable airport. In 2025, 93 lithium-battery incidents involving smoke, fire or heat were recorded. The exact technical source of the smoke aboard DL251 — whether a galley electrical fault, an air conditioning pack, or a personal electronic device — remains unclear as Portuguese aviation safety authorities and Delta continue technical inspections, per Deep Arrival's reporting.
The Porto diversion follows another Boston-bound Delta diversion earlier this year: a flight from Los Angeles diverted to Detroit in August after its captain fell ill mid-flight, Hoodline previously reported.
