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The new timetable is the most pessimistic to date from customers that also include American and Southwest airlines. Boeing recently halted production of the single-aisle jetliner, involved in two crashes that killed 346 people, which it hasn't been able to deliver to customers since March.
The best-selling model in Boeing's history, the Max is the latest version of an airliner introduced in 1967 and was designed at a time when jet fuel prices were spiking to be more fuel-efficient than its predecessors. Deliveries of the planes didn't start until mid-2017, and only about 70 were flown by U.S. carriers when the Federal Aviation Administration told airlines not to use them while a fix for anti-stall software linked to both crashes was developed.
"Pushing our timeline back to early June is what is best for our customers and our operation," said Frank Benenati, a spokesman for Chicago-based United. By moving the return-to-service date back more than just a month -- as we have done previously throughout 2019 -- it allows us to have more certainty by providing our customers and our operation a firmer and more definitive timeline."