An American Airlines Boeing 757 that made an emergency landing in West Palm Beach, Fla., Wednesday, may have had a problem with a cockpit window heater that has affected at least five other 757s since 2004. The plane was flying from San Juan, Puerto Rico to Philadelphia when the cockpit filled with smoke, the NTSB said in a news release. As the plane descended, the inner pane of the first officer’s window shattered. Photographs taken after landing showed the heating unit attached to that window burnt and partially melted, with cracks in the window radiating from it. Last year, the NTSB recommended the FAA mandate different heating systems in all Boeing 747, 757, 767 and 777 planes. While the FAA never followed up with that, it noted that Boeing recently issued a voluntary service bulletin that would address the issue in many of the planes.