Delta Air Lines Inc. says some of its aircraft have been flown with engines using improperly documented components, a disclosure indicating the extent to which parts linked to a British distributor have been uncovered.

Suspect components were found on only one engine of the planes that were flown, a company spokesman said Tuesday, declining to quantify exactly how many aircraft and engines were impacted.

The information comes from a new assessment of Delta’s ongoing internal investigation into the airline’s use of the uncertified parts, which it first disclosed on Monday.

Read more: Delta Says Some of Its Jet Aircraft Engines Used Fake Parts

Delta and several other carriers have disclosed that engines in their fleet used parts distributed by AOG Technics Ltd., a London-based company at the center of probes by regulators into allegedly fake parts. The uncertified components were used in a popular type of jet engine made by CFM International Inc., a joint venture of General Electric Co. and Safran SA.

--With assistance from Ryan Beene.

(Corrects third paragraph to indicate Delta first disclosed the issue on Monday.)