(Reuters) - U.S. supplier Spirit AeroSystems ( SPR ) is investigating years of record-keeping of parts for multiple plane programs, after discovering cases of missing and duplicate paperwork, two industry sources told Reuters.

The Wichita, Kansas-based supplier has checked paperwork and hundreds of thousands of parts dating to 2010, the earliest date for its records, after discovering anomalies last month in reports from a machine that measures parts, one of the sources said.

At this time, Spirit's investigation has not identified any potential safety concerns with the affected parts, said the two sources familiar with the matter, who spoke on condition of anonymity. 

Spirit Aero spokesperson Joe Buccino confirmed Spirit has notified affected customers and is investigating internally.

The missing records accounted for 4% of all records since 2010 on parts measured by a coordinate measuring machine (CMM), which is used to precisely measure parts such as brackets, frames, and beams. 

Buccino said in a statement that the company "has discovered a relatively small number of parts delivered where we are unable to produce valid coordinate measuring machine reports, spanning several customer programs since 2010."   

The sources provided supplementary details, with one adding that the company is expected to tell customers if parts might need additional inspections or replacement. 

Paper trails are critical in aviation. Regulators insist on clear documentation for even minor production changes to assure planes are safe. Missing, duplicate or false paperwork can lead to costly, labor-intensive investigations for manufacturers and suppliers.

Spirit produces aircraft parts for commercial and defense companies including planemaker Airbus and Boeing ( BA ), which is set to acquire the company for $4.7 billion. 

Boeing ( BA ) declined comment while Airbus was not immediately available for comment.

The U.S. Federal Aviation Administration said its regulations require manufacturers to maintain records for products they produce to ensure they comply with safety standards. The FAA reviews these records as part of safety oversight. 

One Spirit customer said they were not concerned because the affected parts were built into a system that has backup measures or redundancies.

The issue was first flagged to Spirit by an employee who detected some anomalies in a few CMM reports, which sparked a broader investigation by Spirit that turned up missing and duplicate reports, one of the sources said. What caused the issue is not clear. 

Spirit is moving to automate certain steps to produce and store CMM reports to eliminate any improper actions by human operators. Spirit aims to have this solution in place in the next 90 days, the source said.