Checks are to be carried out on a second Boeing aircraft model following the blowout of an unused door on one of its planes earlier this month.
BBC News report the US Federal Aviation Administration said January 21 that airlines should also inspect older 737-900ER models, which use the same door design as the 737 Max 9 airplane whose cabin panel broke away thousands of feet above the ground January 5.
The FAA described the move as an "added layer of safety".
It said there had been no reported issues with the 737-900ER, but that it uses the same style of panel to "plug" an unused door. The FAA did not order the older model to be grounded while the visual inspections are carried out by operators, as it did with the 737 Max 9 planes.
The agency is investigating the firm's manufacturing practices and production lines, including those linked to subcontractor Spirit AeroSystems, which provided the panel.
Boeing has said it will increase the quality of inspections in its manufacturing process in wake of the incident.
The 737-900ER models have carried out 11 million hours of operations without similar incident to the newer 737 Max 9s.
