A Delta Air Lines flight from Josep Tarradellas Barcelona–El Prat Airport (BCN) to Boston Logan International Airport(BOS) was forced to turn around mid-flight over the Atlantic Ocean on Sunday and made an emergency landing in Portugal. Delta flight 251 was not far off the northeast coast of Spain when smoke in the cabin prompted the pilots to declare an emergency. The pilots were directed to land the Airbus A330-300 at Francisco Sá Carneiro Airport (OPO) in Porto, Portugal.

Flight 251 was carrying 283 passengers and 13 crew members. According to a spokesperson ​for ⁠Portugal’s Emergency and Civil Protection Authority, eight passengers were treated and released upon landing, while three others were transported to a local hospital. FlightRadar24 tracking data shows DL251 had departed BCN at 3:15 PM local time (13:15 GMT) and arrived at OPO at 5:45 PM local time (16:45 GMT). An Instagram post containing ATC audio reveals that nearly a dozen passengers were affected, with two flight attendants using supplemental oxygen during the diversion to Porto.

Delta Cites A Mechanical Issue As Reason For Diversion

Credit: Flickr

According to a statement released by the airline, “the flight landed safely, and we apologize to our customers for the delay in their travels as we work to get them to Boston as safely and quickly as possible.” Delta attributed the diversion to a mechanical issue, without providing further detail.

The Airbus A330-300 involved in the incident, N824NW, was built in 2015 and is powered by two General Electric CF6-80 engines. The CF6 is a very popular engine, used by commercial jet manufacturers on older widebody jets including the Airbus A300, A310, and A330-200 and -300 series. Boeing also has used CF6 variants on its 747 and 767 models. McDonnell Douglas used the CF6 on its DC-10 and MD-11 aircraft, which are no longer in production.

What Causes Smoke Or Fumes In The Cabin?

Credit: Airbus

All commercial jets have a “bleed air system” that serves several important functions. It turns hot engine air into cool air to keep the cabin comfortable. It is used to push hot air along the leading edges of the wings to prevent and remove ice, which will cause a disturbance in air flow. It also pressurizes potable water tanks and hydraulic reservoirs.

If a problem with the bleed air system occurs, it can send smoke or fumes into the cabin. When a carbon seal in the engine fails or becomes damaged, it can allow oil to leak into the engine’s compressor system, creating smoke that can be ingested and distributed into the air conditioning system. Because the pilots can’t immediately know whether the smoke or fumes are toxic, they will often declare an emergency and land at the nearest airport out of an abundance of caution.

“Fume Events” Becoming More Common For Airbus

Credit: Photo: Airbus

Incidents have become more common in recent years on Airbus aircraft in recent years involving smoke or fumes in the cabin. A Delta flight from BOS to London Heathrow Airport (LHR) with an Airbus A330neo was forced to return due to a mysterious odor in the cabin last Thursday. Earlier this month, A Swiss International Airlines Airbus A330-300 flight from Zurich Airport (ZRH) to New York JFK Airport (JFK) had to divert to Bangor International Airport (BGR) in Maine after smoke engulfed the business class cabin.

Flight attendants have been vocal about Airbus fume incidents, particularly on the A320 series. In April 2025, a United Airlines flight attendant sued Airbus, due to injuries allegedly suffered from contaminated cabin air. That case was dismissed. A 2015 report published by the Federal Aviation Administration (FAA) found that the rate of reported aircraft fume events was less than 33 per million departures.