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Boeing's checklist of 737 Max fixes grows with wiring issue

DALLAS — Boeing faces a growing checklist of items it could be forced to fix before federal safety officials let the grounded 737 Max airliner fly again.

The Federal Aviation Administration recently asked Boeing to review all possible ramifications of the changes it is making on the plane. During that review, Boeing discovered that bundles of electrical wiring in the plane were too close together and — at least in theory — raise the potential for a short circuit that could cause pilots to lose control of the plane.

“We identified this wiring-bundle issue … and we are working with the FAA to perform the appropriate analysis,” Boeing spokesman Gordon Johndroe said Monday.

The company said, however, it is too soon to know whether it will need to make any design changes, such as moving the wiring bundles farther apart. Boeing says it believes that other safeguards, including circuit breakers and insulation around the wiring, could be sufficient to prevent a short-circuit from leading to another crash.

The discovery of the wiring issue was first reported by The New York Times.

Boeing built and delivered nearly 400 Max jets to airlines before the plane was grounded in March after two crashes that killed 346 people. Since then, another 400 or so Max jets have rolled off the assembly line, although they can’t be sent to airlines.

Boeing engineers have finished changes to a key software system called MCAS that was activated by faulty sensors in each crash, firmly pushing the noses of the planes down, a condition called runaway stabilizer.

The recent review of changes to the Max raised the question whether a wiring short circuit could also cause a runaway stabilizer.

Boeing has been working for more than a year to fix MCAS, which was designed partly to prevent the plane from aerodynamic stalls that could cause it to fall from the sky. Boeing is making the system less powerful and linking it to two sensors instead of one for extra protection against the kind of sensor failures that occurred before the crashes in Indonesia and Ethiopia.

Separately, in June FAA test pilots were able to cause a failure of flight computers on the Max during a simulator test.

It is unclear when the Max will be cleared to fly. On Monday, FAA spokesman Lynn Lunsford repeated the agency’s position that it has no timetable for reviewing the plane. He said the FAA and Boeing are analyzing findings from the recent review of Boeing’s changes to the plane, and “the agency will ensure that all safety related issues identified during this process are addressed before the aircraft is approved for return to passenger service.”

David Koenig, The Associated Press