Flight systems, however, typically are built with a

 backup system so there can be no single point of failure. Since the crashes of Max jets in Indonesi

a in October and Ethiopia last month, Boeing has modified design of the anti-stall device to include two sensors on all aircraft.

The FAA allows airlines to make minor modifications in previously certified

aircraft to meet their operational needs, a rule Boeing followed in building the 737 Max for

foreign carriers. Ethiopian Airlines and Indonesia’s Lion Air — involved in fatal crashes five months apart — repo

rtedly declined to buy two add-on safety devices that might have helped the pilots keep the doomed planes in the sky.

Neither airline purchased the “angle of attack” system display for readi

ngs of two sensors rather than one and a “disagree light” to be activated if the sensors prod

uce conflicting readings. The Lion Air crash in October killed 189 passengers and crew.

Airlines around the world, including China and the US, have flown the 737 Max, introduced in 2018, without incident.

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