CNN  —  At least two major airlines have warned pilots that if a bird hits one of the engines on a Boeing 737 Max, the passenger cabin could become filled with smoke. Documents newly obtained by CNN detail that Boeing warned Southwest Airlines and American Airlines of the potential problem in February and both airlines in turn sent alerts to their respective pilot groups. “Boeing has received two reports of CFM LEAP-1B engine failures following large bird strikes on takeoff and initial climb,” said the alert to American Airlines pilots. Southwest’s alert says such a strike could cause oil to burn and the “immediate presence of smoke and fumes” entering the passenger cabin “through the air conditioning system.” The issue was not made widely public until being first reported by The Seattle Times but is significant as it could signal another potential issue with 737 Max aircraft which have been dogged by manufacturing and design issues. Engine maker CFM International says their engine has met “bird ingestion certification requirements, and the engines performed as designed during these events.” The company underscored that birds in the two incidents that prompted pilot bulletins were much larger than required for certification testing and that the CFM engine still performed as designed. The Federal Aviation Administration says it “will continue working with Boeing on the investigation into these incidents and will determine if additional actions are required based on the findings.” Boeing says it issued a service bulletin in February “after two bird strike incidents” and has been working with engine manufacturer CFM “to learn more about this matter and we are keeping the FAA and our operators informed of any learnings.” On Tuesday, outgoing Boeing CEO Dave Calhoun told lawmakers on Capitol Hill that he accepts responsibility for the plane maker’s recent failures, including a door plug blowout on a 737 Max 9 and the crash of two 737 Max 8s that killed 346 people abroad.