United Airlines has found loose bolts on door plugs of several Boeing 737 Max 9 planes during inspections spurred when a panel of that type blew off an Alaska Airlines flight last week, according to a person familiar with the matter.

United didn’t immediately comment.

The Federal Aviation Administration on Saturday grounded dozens of 737 Max 9s after the panel blew out midflight on Alaska Flight 1282.

Plane manufacturer Boeing said earlier Monday it issued instructions to airlines to conduct the inspections of the Max 9s in their fleets.

Alaska Airlines, which is also inspecting its planes, didn’t immediately comment. Aviation publication The Air Current earlier reported that United had discovered the loose bolts.

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