The US Federal Aviation Administration (FAA) has recommended operators of Boeing 737-900ERs fitted with mid-cabin door plugs to inspect the aircraft to ensure they are properly secured as investigations continue into the in-flight loss of a plug from an Alaska Airlines Max 9 on 5 January. In a safety alert for operators issued on 21 January, the FAA is encouraging 737-900ER operators to " conduct a visual inspection to ensure the door plug is restrained from any movements through the two upper guide track bolts and two lower arrestor bolts", and report their findings. "The Boeing 737-900ER mid-exit door plugs have an identical door plug design to the 737-9 Max," the FAA states. "As part of their Safety Management Systems, some operators have conducted additional inspections on the 737-900ER mid-exit door plugs and have noted findings with bolts during the maintenance inspections." The FAA adds that it is continuing to evaluate data involving the mid-cabin door plug and will determine if additional actions are required. As it was issued in a safety alert, the inspections are not mandatory yet, but are likely to be conducted by 737-900ER operators globally that have mid-cabin exit plugs fitted. Fleets data shows that there are 490 -900ERs in service and 14 in storage. Delta Air Lines is the largest operator of the type globally, with 160 in service and three stored, followed by United Airlines which has 136 in service. Alaska Airlines also has 79 -900ERs in service.

Frontier Airlines plans to open a new crew base at San Juan's Luis Munoz Marin International airport in Puerto Rico in June. The low-cost carrier says the base is expected to employ up to 90 pilots and 200 flight attendants during its first year of operation. It adds that combined with airport and maintenance positions, it will likely generate about $84 million annually in local wages, with further growth expected in the coming years. "Our base will provide significant economic impact and new jobs for Puerto Ricans," states Frontier Airlines chief executive Barry Biffle. "A crew base also helps support smooth flight operations, benefiting customers flying to and from the island who will have access to a wide variety of destinations, including a number of underserved markets, as we continue to grow our Puerto Rico operations." It will be Frontier's 13th crew base.

Indonesia has given the green light for Lion Air to operate its three Boeing 737 Max 9s again after grounding them following the Alaska Airlines door-plug blowout accident on 5 January. The country’s transport ministry grounded the jets on 6 January but lifted it on 11 January after checks by Lion confirmed that emergency doors installed on the three jets were not affected by US Federal Aviation Administration airworthiness directive, its Directorate General of Civil Aviation said. The carrier is the only operator of the type in the southeast Asian country. Lion had said previously that its Max 9s have operational mid-cabin emergency exit doors, unlike the aircraft involved in the Alaska accident, which uses a mid-cabin door plug. Fleets data shows it has two 737 Max 9s stored – PK-LRF (MSN 42989) and PK-LRG (MSN 42991) – and one – PK-LRI (MSN 42987) – in service. Since the grounding was lifted on 11 January, one jet (PK-LRI) has been deployed on a domestic flight between Jakarta and Makassar on 14 and 15 January.