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.

US safety investigators have warned over a safety issue with a vibration-reduction feature on the CFM International Leap-1B turbofans that power the Boeing 737 Max which can cause smoke to enter the cockpit.

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.