The Federal Aviation Administation (FAA) has asked Boeing to supply fresh analysis and documentation demonstrating that 737 MAX subsystems would not be affected by electrical grounding issues.

Reuters reports that the issues were first flagged up in three areas of the jet in April, resulting in the suspension of nearly a quarter of the 737 MAX fleet. The FAA has issued an airworthiness directive requiring the issue to be fixed before the aircraft can resume flight. Boeing has reported that the issue affects 109 in-service planes worldwide with Reuters sources putting the figure of 300 affected planes within Boeing’s inventory.

US airlines were expecting Boeing to release service bulletins this week which would allow them to return the aircraft to service following alterations. The latest requirement for further analysis is likely to lead to add further uncertainty over the return to service of the affected planes. Reuters’ sources said the service bulletins advised airlines on how to fix the problems with grounding, or the electrical paths designed to maintain safety in the event of a surge of voltage.

FAA reviewing Boeing’s analysis and revisions

The service bulletins had been approved by the FAA but, during ongoing discussions with Boeing, the regulator requested additional analysis over whether other jet subsystems would be affected by the grounding issue. The FAA is said to be reviewing Boeing’s analysis and necessary revisions to the service bulletins before they can be sent to airlines.

A Boeing spokeswoman said.“We continue to work closely with the FAA and our customers to address the ground path issue in affected 737s.”

An FAA spokesman confirmed the regulator was “continuing to work with Boeing.”

Planes taken out of service due to electrical grounding issue

Dozens of 737 MAX jets were taken out of service last month after Boeing warned of a production-related electrical grounding problem in a backup power control unit situated in the cockpit on some of its recently built aircraft. The issue, which has also stalled the delivery of new aircraft, was then found in two other places on the flight deck, including the storage rack where the affected control unit is kept and instrument panel facing the pilots.

Reuters has reported that Boeing had proposed adding a bonding strap or cable that workers can screw onto two different surfaces creating a grounding path. Airlines had initially been told that the alteration could take between hours or a few days per jet.

The entire 737 MAX fleet was grounded for nearly two years in 2019 after two fatal crashes.

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