Boeing 737 Max, June 20 -- US safety investigators have called for urgent action regarding an engine issue on the Boeing Co. 737 Max aircraft that could fill the cockpit and cabin with smoke.

The National Transportation Safety Board's recommendation comes after two such incidents were reported in which planes were filled with smoke after large birds struck their engines.

Both incidents involved 737 Max aircraft flown by Southwest Airlines and powered by Leap-1B engines made by CFM International, which is a joint venture of GE Aerospace and Safran SA. The NTSB connected the incidents to a malfunction with one of the engine's key safety features.

In both cases, damage to the fan blades following the bird strikes activated a safety featur...