CHICAGO, IL -- Boeing says the debris it found inside fuel tanks of 737 Max planes built in the past year is unacceptable.
The company says the debris includes rags, tools, metal shavings and other materials left behind by workers during production of the troubled plane.
That fleet has been grounded nearly a year after two crashes internationally killed 346 people.
The company is still building the planes, about 40 a month, hoping they will return to the skies this summer.
Boeing's new CEO says correcting problems that left debris in the fuel tanks of some 737 MAX jets built in the past year but not yet delivered will be a matter of better production discipline.
David Calhoun also told KING-TV in Seattle, Washington, that Boeing's decision to ask Washington to suspend its preferential state Business and Occupation tax rate to meet European Union requirements shouldn't hurt Boeing.
Calhoun was in Seattle for a test flight on a modified 737 MAX. Calhoun says Boeing is trying hard to cooperate with the Federal Aviation Administration as it works to get the grounded 737 MAX recertified.
Calhoun said the FAA's requests have been reasonable.
FAA Chairman Steve Dickson has said the 737 MAX will be the most vetted plane in aviation history when it's approved to fly again. Calhoun said he thinks the MAX will be recertified sometime this summer.