Boeing has suspended 737 MAX flights after being informed by CFM International of a potential issue with the aircraft’s LEAP-1B engine, although Boeing says MAX 8 deliveries will begin this month as planned.

“CFM has notified us of a potential manufacturing quality escape with low pressure turbine (LPT) discs in LEAP-1B engines delivered to Boeing,” Boeing said in a statement.

“We are working with CFM to inspect the discs in question. CFM and its supplier notified us after discovering the issue as a part of their quality inspection process. At no time have we experienced an issue associated with the LPT during our ongoing MAX testing program.”

Boeing said the decision to suspend MAX flights was made “out of an abundance of caution.”

The suspension comes just as Boeing was preparing to begin delivery the 737 MAX 8, which was certified in March, to airlines. Malaysia’s Malindo Air is expected to receive the first delivery. The aircraft is also expected to enter service this summer with Norwegian. “Our plan remains to begin MAX deliveries in May,” Boeing said, adding that there will be no halt in MAX production or in production and deliveries of 737NG aircraft.

The suspension also comes less than a month after the 737 MAX 9 achieved first flight.

Boeing emphasized that it has had no problems associated with the LEAP-1B in flight testing. “The MAX 8 flight test program put over 2,000 hours on the engines, including abuse testing and flights lasting over 9 hr., undergoing thorough inspections throughout,” Boeing stated.

“Additionally, 180-minute ETOPS testing completed in April 2017 required another 3,000 simulated flight cycles on the test stand before a complete inspection was conducted by CFM. The LEAP-1B and 737 MAX [8] have been certified to the most stringent requirements in commercial aviation.”

A CFM spokesperson noted the potential issue was not discovered in flight testing or on any aircraft out in the field, but during a quality inspection in the factory, and the decision to suspend flights was made out of caution.

CFM is a GE Aviation/Safran Aircraft Engines joint venture. The spokesperson added that CFM has two suppliers for the LPTs used on the LEAP-1B, and the potential issue is only with one supplier’s LPT. The CFM LEAP-1A engine powering Airbus A320neo family aircraft is not affected by the potential issue.