(WJW) – Boeing is asking airlines to check for loose bolts within the rudder control system of its 737 MAX airplanes, the Federal Aviation Administration confirmed Thursday.

The announcement stems from the discovery of a bolt with a missing nut during a routine inspection of “a mechanism in the rudder-control linkage,” the FAA said.

“The company discovered an additional undelivered aircraft with a nut that was not properly tightened,” the agency added.

Carriers that have 737 MAX aircraft in their fleet — Alaska Airlines, American Airlines, Southwest Airlines and United Airlines — are now being instructed to examine the “specific tie rods that control rudder movement for possible loose hardware,” according to the FAA.

Boeing estimates the inspections to take around two hours per plane. Aircraft operators also routinely conduct tests prior to takeoff that would alert them to any issue with the rudder, Boeing added.

A representative for Boeing, in a statement shared with Nexstar, said the manufacturer will remain in contact with the FAA amid inspections.

“The issue identified on the particular airplane has been remedied,” Boeing said. “Out of an abundance of caution, we are recommending operators inspect their 737 MAX airplanes and inform us of any findings. We informed the FAA and our customers and will continue to keep them aware of the progress.”

No safety issues have been reported as a result of possible loose bolts, according to Boeing.

The FAA said it is closely monitoring the inspections and will stay in contact with Boeing during the process.

According to Boeing’s website, the 737 MAX airplane “offers excellent economics, reducing fuel use and emissions by 20% while producing a 50% smaller noise footprint than the airplanes it replaces.”