The US Federal Aviation Agency is calling for a "visual inspection" on another Boeing 737 model amid increasing concern on the aircraft's flight worthiness.

The aviation agency recommended inspections on door plugs installed on Boeing 737-900ER planes, a much more older model than the 737 Max 9 that was involved in an airway incident earlier this month.

FAA Cites Safety Protocol for 737-900ER Inspection

According to the FAA, the 737-900ER has a similar door plug design as the 737 Max 9. The agency, however, assured that the door plugs in the 737-900 has not yet faced similar issues.

The FAA reasoned the inspections as "an added layer of safety." Several airlines have since conducted additional inspections on their planes.

Boeing has expressed support to the FAA's statements.

The Boeing 737-900ER is among the list of most used Boeing aircrafts with a total 11 million operation hours and nearly four million flight cycles across all airlines, according to the FAA.

Also Read: Boeing 737 MAX 9 Aircraft Temporarily Suspended Worldwide by FAA

Boeing 737 Models Face Scrutiny Over January Flight Incident

The Boeing 737 aircraft has been under a lot of scrutiny over the past month as the aircraft's flight worthiness is put into question.

It can be remembered that a similar model used by the Alaska Airlines suddenly have its cabin panel blow out midflight on Jan. 5, forcing the aircraft to make an emergency landing.

Although no one was seriously hurt by the incident, several passengers have already filed a lawsuit against Alaska Airlines and Boeing for negligence over safeness of their aircrafts.

It is worth to note that the 737 Max 9 model was first released in 2012, still far from its out-of-commission date at least 30 years after manufactured.

Some of the 737 Max 9 models are still suspended as the FAA continue its inspections. The FAA said the initial batch of 40 aircraft has already passed inspections.

Related Article: Boeing 737 MAX Incident Contributes to Biggest Flight Disruption in 6 Months