The National Transportation Safety Board warned that certain CFM engines installed in some Boeing 737 Max jets may feed smoke into the cockpit or cabin after a bird strike.

The recommendations were inspired by two incidents on Southwest Airlines flights, when engines malfunctioned after bird strikes and poured smoke into the cabins.

The 737 MAX series has faced intense public scrutiny since two fatal crashes in 2018 and 2019 killed a total of 346 people. While those accidents were linked to faulty sensor data and a flawed flight control system, the recent incidents have continued to raise concerns about the aircraft’s reliability.