Ever since an Alaska Airlines  (ALK) – Get Free Report plane had a door and window panel blown out seven minutes after a flight’s takeoff at the start of January, the aviation industry has been dealing with the impact of the FAA grounding nearly 200 Boeing 737 Max 9  (BA) – Get Free Report planes for inspection of how this could have happened. 

Airlines such as Alaska and United Airlines  (UAL) – Get Free Report, which had many of this type of plane amid their fleet, had to completely rework their route networks due to not being able to run the flights they normally with so many planes out of commission.

Related: These are the flights affected by the 737 Max 9 grounding

This week, United and Alaska Airlines reported that they have received instructions on inspecting their aircraft from the Federal Aviation Administration (FAA). Inspecting individual aircraft is the final step before flights on them are cleared to resume. During the inspections to take place over the last two weeks, the FAA was working with Boeing to determine how the “loose bolts” occurred on the parts it supplied.

FAA to ‘proceed with the inspection and maintenance phase,’ spokesperson says

“The exhaustive, enhanced review our team completed after several weeks of information gathering gives me and the FAA confidence to proceed to the inspection and maintenance phase,” FAA Administrator Mike Whitaker said in a statement.

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Each aircraft is to be inspected by a team of engineers for at least six to eight hours and, according to Whitaker’s statement, select ones have been slated to return to the skies “one by one” on Jan. 26.

Whitaker clarified that this does not mean that 737 Max 9 planes will resume flying “business as usual.” No new Boeing product lines or expansion plans will be approved “until we are satisfied that the quality control issues uncovered during this process are resolved.”

Boeing, in turn, said that it will “continue to cooperate fully and transparently with the FAA and follow their direction as we take action to strengthen safety and quality.”

‘Our aircraft will only return to service once the rigorous inspection process is completed’

Airlines, however, celebrated the milestone in returning the grounded planes back to operation while also being careful to reassure their staff and travelers that there has been a thorough inspection process to ensure the nearly catastrophic situation would not happen again.

Over the last two years, Alaska Airlines had made a major investment into new 737 Max 9 planes as part of its efforts to modernize its fleet and currently has 65 in its active fleet while United Airlines has 79 planes. International airlines that rely heavily on the 737 Max 9 include Mexico’s Aeromexico  (GRPAF) – Get Free Report and Panama’s Copa Airlines  (CPA) – Get Free Report.

“Each of our aircraft will only return to service once the rigorous inspections are completed and each aircraft is deemed airworthy according to the FAA requirements,” Alaska Airlines said in a statement. “The inspections are expected to take up to 12 hours for each plane.”

United also sent its staff a note saying that it would “return each MAX 9 aircraft to service once this thorough inspection process is complete” while the actual date that has been floated around is Sunday, Jan. 28.