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

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.

Federal safety officials are pressing for immediate steps to address a potentially serious issue involving Boeing (NYSE:BA) 737 Max aircraft, following incidents where bird strikes triggered engine failures that resulted in smoke filling the cabin and cockpit.