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

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 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 revealed that engines in their fleet used parts distributed by AOG Technics Ltd., a London-based company at the center of probes by regulators into components sold with falsified airworthiness records. 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.

The FAA last month warned US airlines and others in the industry about AOG parts sold with forged airworthiness documentation, following a similar earlier alert by European regulators. Those actions triggered a worldwide search of records to hunt down the AOG-supplied components, which regulators said should be removed from engines immediately. Safran has said it was alerted originally by a European aircraft maintenance provider, who inquired about a part that looked to have a suspicious origin. 

American Airlines Group Inc., Southwest Airlines Co. and United Airlines Holdings Inc. all have found the suspect components on engines, along with Virgin Australia Airlines Pty. 

Delta has declined to say what type of AOG-documented parts it discovered. The “small number” of engines involved account for less than 1% of the more than 2,100 power plants on its mainline fleet, a spokesperson said Monday. The parts were discovered during engine work by an unnamed third party, the carrier said. 

As many as 21 engines could have been affected, according to Bloomberg calculations based on data provided by the airline, which would represent the most among US carriers that have disclosed a number. As many as 96 total engines were impacted by parts supplied by AOG, GE has said.

AOG last month was ordered by a London judge to hand over records to help identify additional suspect parts after GE and Safran filed a lawsuit seeking documents relating to “every single sale of products.”

--With assistance from Ryan Beene.

(Updates with regulator warnings from fourth paragraph. An earlier version of this story corrected date Delta first disclosed the issue.)

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