The Federal Aviation Administration (FAA) on Thursday said 106 Boeing 737 Max airplanes have been grounded worldwide by an electrical issue and said the U.S. planemaker is still working on a fix.
Boeing disclosed an electrical power system issue on April 7 and recommended operators temporarily remove these airplanes from service.
The problem involved the electrical grounding - or connections designed to maintain safety in the event of a surge of voltage - inside a backup power control system. The FAA said Thursday "subsequent analysis and testing showed the issue could involve additional systems."
The FAA said in a formal notice to international air regulators that 106 airplanes are covered by the notice, including 71 registered in the United States. "All of these airplanes remain on the ground while Boeing continues to develop a proposed fix. The FAA is in contact with the airlines and the manufacturer," the agency added.
The FAA said Boeing's investigation showed the issue could impact the standby power control unit, a circuit breaker panel and main instrument panel.
The notice said the "FAA expects to issue an airworthiness directive mandating corrective action before further flight for all affected airplanes."
Boeing did not immediately comment.
The top three U.S. 737 Max operators - Southwest Airlines, American Airlines and United Airlines - removed more than 60 jets from service following the notice from Boeing.
The FAA said other carriers impacted include Cayman Airways, Copa Airlines, GOL Linhas Aereas, Iceland Air, Minsheng Leasing, Neos Air, Shanding Airlines, SilkAir, Spice Jet, Sunwing Airlines, TUI, Turkish Airlines, Valla Jets Limited, WestJet Airlines and Xiamen Airlines.
The FAA said it "verified all operators with affected airplanes have voluntarily taken those aircraft out of service."