The National Transportation Safety Board issued an urgent safety recommendation Wednesday to address the possibility of smoke entering the cockpit or cabin of Boeing 737 MAX airplanes equipped with CFM International LEAP-1B engines.

The National Transportation Safety Board issued a rare, urgent safety bulletin warning of potential problems with the jet engines on Boeing 737 Max aircraft. The recommendation was inspired by two incidents on Southwest Airlines flights that hit birds.

The NTSB issued an “urgent safety recommendation” related to the engine on the 737 MAX after two incidents where smoke entered the cabin.