Boeing is facing a formal investigation into whether it made sure 737 Max 9 planes were “in a condition for safe operation” after a cabin panel blew off during an Alaska Airlines flight.“This incident should have never happened, and it cannot happen again,” the Federal Aviation Administration said, announcing an investigation into whether the planemaker “failed to ensure” the jets complied with safety regulations.The FAA grounded 171 737 Max 9 planes with plug doors over the weekend. “The safety of the flyi ...