Boeing has grounded selected 737 MAX jets over electrical issues, just months after their return to the skies. The manufacturer has advised 16 airlines to address a potential electrical issue in a specific group of 737 MAXs, prior to further operations.

Carriers including Southwest, American Airlines, Alaska Airlines and United scrambled to organise replacement aircraft on Friday; a combined 67 of their aircraft were grounded, to allow for verification that a sufficient ground path exists for a component of the electrical power system.

Boeing could not provide an estimate as to the length of disruption, saying in a statement that “it is premature to estimate the amount of time required as it could take a matter of hours or a few days”. The FAA stated that the issue “could affect the operation of a backup power control unit”.

Southwest announced that they have pulled 30 MAX-8 aircraft from service; adding that they are flying just 15 of their 58 MAXs, but they still expect “minimal” disruption to operations. United withdrew 16 aircraft from service and American Airlines have grounded 17. Alaska Airlines has also grounded all four of their 737 MAXs, according to Bloomberg.

Boeing did not comment on the total number of affected aircraft.