More than 170 737 Max 9 aircraft were grounded by the US Federal Aviation Administration after a cabin panel broke thousands of feet above the ground.
The agency stated on Sunday that since the 737-900ER and older models share the same door design, airlines should also examine them.
The action was referred to by the FAA as a “added layer of safety”.
It stated that while no problems with the 737-900ER had been reported, it did use the same type of panel to “plug” an unusable door as the aircraft that was involved in the horrifying incident on January 5.
A huge hole in the side of the aircraft was left by the panel coming loose, forcing an emergency landing on an Alaska Airlines flight from Portland, Oregon to California.
The incident caused a sharp decline in Boeing’s share price and forced the FAA to ground all 737 Max 9s equipped with that type of panel.
The agency is looking into the company’s production lines and manufacturing processes, especially those connected to the panel’s subcontractor Spirit AeroSystems.
The FAA said earlier this week that it had inspected 40 of the grounded aircraft, but it did not specify when those aircraft would be allowed to take to the air once more.
“The safety of the flying public, not speed, will determine the timeline for returning these aircraft to service,” the agency stated in a statement on Sunday.
In the wake of the incident, Boeing has stated that it will improve the caliber of inspections performed during the manufacturing process.
Compared to the newer 737 Max 9, the 737-900ER models have operated for 11 million hours without experiencing any similar incidents.
The FAA did not mandate that the older model be grounded while operators conducted visual inspections.
