(Reuters) - Spirit AeroSystems ( SPR ) said it has developed a plan that gives it "a high degree of confidence" to meet U.S. planemaker Boeing's ( BA ) rate and quality expectations for parts for the 737 MAX jet, the company told Reuters on Wednesday.

Boeing ( BA ) is under pressure to restore slumping production of its strong-selling narrowbody jet to 38 per month in the second half of the year as the planemaker's credit rating comes under scrutiny from rating agencies.

The company is pressing its key supplier Spirit Aero to improve the quality of the fuselages it produces for the MAX at a higher rate for the second half of the year. Boeing ( BA ) is in talks for a tie-up with Spirit, which is scheduled to report earnings on May 7.

"We've developed a plan that we believe affords us a high degree of confidence that we will meet Boeing's ( BA ) demand rate and quality expectations," said Spirit Aero spokesperson Joe Buccino. "We will have more information on this matter at next week's earnings call."

Boeing ( BA ) was not immediately available for comment.