A French airline has grounded a newly upgraded aircraft built by an Airbus joint venture after its pilots reported cases of suspected fumes leaking into the cockpit and cabin causing migraines and other symptoms during flight. One of the planes affected was being used by Airbus to ferry workers between its factories in France.

The pilot reports and ongoing investigation into suspected air supply issues by the manufacturer, ATR, comes as Airbus and the industry have long disputed claims from crews, medical professionals and aviation safety agencies that oil leaks inside an aircraft's engines can lead to toxic levels of fumes entering the air supply. A Wall Street Journal investigation last year found that leaks of oil and other aircraft fluids into jet engines have surged over the last decade.

What happens at Air Corsica could have implications beyond the French carrier, with the affected ATRs marking the first application of Pratt & Whitney's new engine for regional planes. At issue is whether the reported fumes are an isolated problem-or point to a broader vulnerability in the air-supply system used on nearly every commercial aircraft flying today.

The news

French carrier Air Corsica in recent weeks grounded four of its seven ATR turboprops as the plane maker and Pratt & Whitney, the maker of its engines, investigate the cause.

The move came after pilots said they had repeatedly noticed odors in the aircraft associated with suspected toxic fume events and had experienced migraines while flying the planes, according to people familiar with the decision.

Among the aircraft now parked was a model chartered by Airbus to run shuttle flights between its factories in the west of France and headquarters in the south, according to the people and flight tracking data. Air Corsica, with a fleet of 14 aircraft, has since assigned alternative planes to keep Airbus' shuttle flights running.

Air Corsica said in a statement last week that it was monitoring instances of issues affecting the air conditioning systems on the ATR turboprops and that it was working with the manufacturers to assess the underlying cause. The airline added that "no causal link has yet been formally established between these reports and any specific technical source."

A spokeswoman for ATR said its analysis of the root cause of the issue was continuing, adding that its planes are designed to meet safety standards set by regulators. The company is a 50-50 joint venture between Airbus and Italy's Leonardo.

The context

The affected aircraft are less than four years old and boast new, more fuel-efficient engines developed by Pratt & Whitney that entered into service with Air Corsica in 2022. The propeller planes are typically deployed on regional routes, particularly in Europe and Asia, and are capable of seating between 30 and 78 passengers.

Referred to in the industry as "fume events," incidents are typically caused by oil leaking past protective seals into an engine's compressor section where it is exposed to extreme temperatures and converted into noxious vapors that mix into the air supplied to an aircraft. A recent study by the U.S. Federal Aviation Administration found that even relatively small leaks can release levels of neurotoxic chemicals that exceed U.S. occupational health exposure limits.

Almost every commercial aircraft flying today uses the so-called bleed air system that draws compressed, unfiltered air directly from the engine into the aircraft.

What's next

It isn't yet clear what the underlying cause is of the reported fumes on Air Corsica's fleet, or whether the issue is specific to the airline or reflects a more fundamental flaw with the aircraft or the new engine. Since its introduction, the Pratt & Whitney engine has become the default on new deliveries of ATR's turboprops and has been ordered by operators including FedEx and India's IndiGo.

Spokespeople for Pratt & Whitney and Airbus declined to comment.

One of the affected aircraft from Air Corsica's fleet is currently with ATR at its facilities in Toulouse, France, where the manufacturer is running tests to identify the source of the reported fumes.