The Federal Aviation Administration announced a new order Thursday, highlighting another possible defect with some Boeing 737 Max jets.

In the order, known as an airworthiness directive, the FAA said an international 737 Max operator discovered loose bolts in the rudder control system on one of its planes in December. Boeing subsequently recommended inspections for 737 Max 8, Max 8-200 (a higher-density version of the Max 8) and Max 9 aircraft.

The FAA said 1,299 planes are affected by the order, with 482 of those registered in the U.S. The agency said that all planes were inspected by early January based on Boeing’s guidance before the FAA order went into effect. With this order, Boeing’s previously issued guidance (which was technically suggested to operators by the manufacturer), will become a requirement when the order is officially published in the Federal Register on Feb. 12.

According to the FAA, the missing bolt “migrated” after a washer and nut were missing from its assembly. The agency did not identify which airline first discovered the problem beyond saying that it was not a U.S. operator.

Cruising Altitude: I’ve covered Boeing’s 737 MAX for years. Here’s a rundown of the issues.

The FAA’s statement said that Boeing discovered an undelivered aircraft with a similar issue during its own inspections.

This problem is separate from the missing bolts that apparently contributed to a door plug ripping off an Alaska Airlines fuselage in January while the plane was in flight. This is the latest headache for Boeing as it tries to address concerns with its best-selling single-aisle jet.

Experts maintain that the 737 Max remains safe, though some travelers expressed skepticism to USA TODAY.

The FAA and National Transportation Safety Board continue to investigate the Alaska Airlines incident, and the FAA has increased oversight of Boeing’s production processes in the meantime.

Zach Wichter is a travel reporter for USA TODAY based in New York. You can reach him at zwichter@usatoday.com

This article originally appeared on USA TODAY: FAA orders Boeing 737 Max operators to perform extra inspections