Washington, Jan 13 : The US Federal Aviation Administration (FAA) announced that it will keep Boeing 737-9 MAX grounded for the safety of travellers until extensive inspection and maintenance are conducted and data from inspections is reviewed. In an online statement on Friday, the FAA said that it determined it needed additional data and is requiring Boeing to provide it after reviewing the aircraft manufacturer's proposed inspection and maintenance instructions, reports Xinhua news agency. Accordingly, the FAA is requiring plug-door inspections of 40 aircraft. If Boeing's inspection and maintenance instructions are approved, operators will be required to perform that regimen on every aircraft before it is returned to service, the FAA said. The FAA decisively grounded approximately 171 Boeing 737-9 MAX planes on January 6 after Alaska Airlines Flight 1282, a 737 MAX 9, lost a mid-cabin exit door plug while it was in flight. The mid-cabin door plugs the aircraft became dislodged following an abrupt depressurisation shortly after departure on January 5. As a result, a piece of the fuselage was expelled at an altitude of 16,000 feet. The plane, bound for Ontario, California, executed an emergency landing in Portland just 20 minutes after takeoff. The agency has launched an investigation to determine if Boeing failed to ensure that completed products conformed to its approved design and were in a condition for safe operation in compliance with FAA regulations. The FAA said it will continue to support the National Transportation Safety Board's investigation into Alaska Airlines Flight 1282, which is independent of its own investigation. The two airlines that operate Boeing 737 Max 9 in the US -- Alaska Airlines and United Airlines -- later found either loose hardware or bolts in the assembly of door plugs on their aircraft. /IANS