Safety analysts last week recommended that the engines on Boeing’s troubled 737 Max airplanes be modified quickly to prevent smoke from filling the cockpit or cabin after a safety feature is activated following a bird strike.

The problem detailed by the National Transportation Safety Board emerged after two bird strikes involving Southwest Airlines planes in 2023: one in Havana, Cuba, and another in New Orleans. The Federal Aviation Administration and Boeing already warned airlines and pilots about the problem and the engine maker has been working on a fix.

The NTSB said that the engines CFM International makes for the Boeing plane inadvertently can release oil into the hot engine when the safety feature, called a load reduction device, is activated after a bird strike or similar engine issue. The resulting smoke feeds directly into either the cockpit or passenger cabin depending on which engine was struck.

Similar engine models with the same safety feature also are used on Airbus A320neo planes and C919 planes made by the Commercial Aircraft Corporation of China. The NTSB urged European and Chinese aviation safety regulators to evaluate those engine models to determine if they also could be susceptible to the smoke problem.

The new safety device that CFM added to its engines solved one problem by limiting damage when an engine starts to come apart, but created a new problem by releasing the oil that burns and generates smoke.

“This is a case of an unintended consequence of a new and innovative safety idea where if the fan gets unbalanced that this is a way to alleviate the load and thereby doing less damage to the engine, the engine pylon, all of that,” said aviation safety expert John Cox, who is CEO of the Safety Operating Systems consulting firm.

CFM said in a statement that it is “aligned with the NTSB’s recommendations and the work is already underway, in close partnership with our airframers, to enhance the capability of this important system.” The company, which is a joint venture between GE Aerospace and Safran Aircraft Engines, confirmed it is working on a software update for the 737 Max’s engines and said it is evaluating similar engine models.

Boeing said it is working with CFM on the update and the planemaker supports NTSB’s recommendations. Boeing also updated some of the checklists pilots rely on to help them take appropriate actions.

The NTSB investigated a December 2023 incident in which a Southwest Airlines plane struck a bird while taking off from New Orleans and had to land quickly after thick smoke filled the cockpit, even making it hard for the pilot to see the instrument panel or his copilot.

In an incident nine months earlier involving another Southwest 737 Max, smoke filled the cabin after a bird strike after takeoff in Havana.