A manufacturing issue has pulled some Boeing 737 Max planes from service

The problem is unrelated to the jet's infamous MCAS software bug.

Mike Blake / Reuters

It was only late last year that the Boeing 737 Max returned to service, but the long-troubled passenger jet has run into another problem. Per Reuters, US airlines temporarily grounded more than 65 737 Max planes after Boeing notified 16 carriers of a manufacturing issue that could affect the model's backup power control unit.

The issue is unrelated to the Maneuvering Characteristic Augmentation System (MCAS) software that grounded the 737 Max for nearly two years after it was linked to two fatal crashes that killed 346 people. According to Reuters, the problem affects about 90 planes. Southwest Airlines took 30 of its 737 Max jets off its flight schedule, the most of any US carrier. Boeing reportedly told the airlines refitting the affected aircraft could take between a few hours and a couple of days. "Boeing has recommended to 16 customers that they address a potential electrical issue in a specific group of 737 Max airplanes prior to further operations," the company said in a statement. "The recommendation is being made to allow for verification that a sufficient ground path exists for a component of the electrical power system."

An analyst Reuters spoke to suggested that it's unlikely the problem is a design oversight given that it seems to affect only a portion of all the Max jets currently in service. Still, it's another setback for a plane that has already had its share of high-profile problems.