The National Transportation Safety Board (NTSB) issued an urgent warning on Wednesday about the potential for certain jet engines, when damaged, to allow smoke to enter the cockpit or cabin.

The NTSB safety bulletin warned about CFM International LEAP-1B engines but encouraged evaluation for LEAP-1A and -1C engines. These engines are used on Boeing 737 Max narrow-body passenger jets and on certain Airbus A320neos, according to a press release.

The NTSB recommendations follow two incidents on Southwest Airline flights when birds flew into the engine and cause smoke or vapor fog.

In March 2023, birds flew into the right engine of a flight departing Havana, Cuba, and caused vapor fog to fill the passenger cabin. In December 2023, a bird flew into the left engine of a flight departing New Orleans, La., and filled the flight deck with what the crew described as “acrid white smoke” that was so thick that it made it difficult to see the instrument panel.

There were no injuries reported on either flight, but the NTSB issued the safety warning because of concerns “that flight crews operating these airplanes may not be fully aware of the potential hazard of” a “smoke-related event along with the appropriate mitigation actions.”

“The FAA agrees with the NTSB recommendations,” the FAA said in a statement, noting Boeing “alerted affected operators” in 2024 to the potential engine issue.

The FAA also alerted operators earlier this year “to reinforce the importance of several factors.”

“These include evaluating their procedures and crew training to ensure they address this potential issue, and evaluating whether training simulators are producing the correct response to an engine failure that would trigger the Load Reduction Device,” the FAA added in a statement.

The FAA said that once the engine manufacturer “develops a permanent mitigation,” the FAA will require operators to implement the change “within an appropriate timeframe.”

“We are 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,” GE Aerospace said in an emailed statement to CNN.

“CFM International and Boeing have been working on a software design update. We support the NTSB’s recommendation,” Boeing said.