WASHINGTON, Jan 11 (Reuters) - The Federal Aviation Administration said Wednesday it is launching a formal investigation into the Boeing 737 MAX 9 after a cabin panel loss led to an Alaska Airlines emergency landing Friday.

The FAA said the Alaska Airlines MAX 9 incident "should have never happened and it cannot happen again." It told Boeing of the investigation in a letter Wednesday "to determine if Boeing failed to ensure completed products conformed to its approved design and were in a condition for safe operation in compliance with FAA regulations" and after learning of "additional discrepancies."

Boeing’s manufacturing practices "need to comply with the high safety standards they’re legally accountable to meet," the FAA added. (Reporting by David Shepardson,Editing by Franklin Paul)