The glitch concerns the intermediate pressure compressor on a “small number” of Package B Trent 1000 engines for the Boeing plane, London-based Rolls-Royce said in a statement Monday.

Following an agreement with the U.S. manufacturer and regulators, some 166 engines that are potentially affected will undergo a one-time inspection to assess the extent of the problem, Rolls said. Package B turbines have been in service since 2012, and evidence of wear has been detected on “high life” examples, it added.

While the check-up visits will incur “some additional cost,” Rolls-Royce stood by its 2018 free-cash-flow estimate of 450 million pounds (RM2.41 billion), plus or minus 100 million pounds. The reiteration takes into account increased servicing of Package C engines, where the glitch was originally detected, as well as mitigating actions being taken across the group, the company said.

Chief Executive Officer Warren East has said Rolls-Royce will reduce discretionary spending to offset the additional funds needed for overhauls and to keep to a key target of reaching 1 billion pounds in free cash flow by 2020.

The engine maker is due to unveil a new restructuring plan authored by turnaround consultant Alvarez & Marsal at a capital markets day this week.

About 80% of the Package C engine version has undergone initial checks for cracking or signs of wear and tear on turbine blades, a person with knowledge of the issue has said. Just under a third of those engines failed the initial inspections required by regulators for planes that fly more than 2 hours and 20 minutes from the nearest diversionary airport.