WASHINGTON — An earlier generation of the Boeing 737 may have issues similar to the door plug that flew out of the side of a recently made plane earlier this month.

The US Federal Aviation Administration Sunday urged airlines operating the Boeing 737-900ER to conduct inspections of the panel that plugs the hole where a mid-plane exit would be and the bolts intended to hold the panel in place.

Since the incident on a newer Boeing 737 Max 9 just over two weeks ago, some airlines have inspected the earlier-built planes and observed “findings with bolts,” the agency said. The FAA did not specify what the findings were. After recent inspections of the newer Max 9s, United Airlines and Alaska Airlines have both found loose bolts.

The FAA noted that the two generations of aircraft “have an identical door plug design.”

The FAA notice does not ground the earlier generation of plane. Instead, it recommends that airlines inspect the four bolts that are intended to hold the door in place “as soon as possible.”

The newer Max 9 aircraft continue to be grounded in the United States. The agency said it continued to review data collected from inspections of 40 sample aircraft as it considered how to determine if the planes were safe to fly again. — CNN