French aerospace supplier Safran SA said it can’t quantify the magnitude of a widening scandal involving suspect unapproved parts on one of its engines, potentially complicating the investigation into components with falsified certificates that found their way onto the world’s most widely flown power plant.

Speaking to reporters on Friday, Safran Chief Executive Officer Olivier Andries said the aircraft parts industry is an “open market.” His company had no prior relationship with London-based AOG Technics Ltd., the supplier at the heart of the case, until it was alerted by an airline, the CEO said, adding that about 100 engines have been identified as having questionable parts.

“We don’t know who they sold those parts to and whether all airlines have done their checks,” Andries said in Paris. “I can’t tell you what I don’t know.”

Andries’s comments come shortly after the US Federal Aviation Administration warned airlines and other industry players that AOG improperly sold parts for a longstanding type of jet engine from CFM International Inc., the joint venture of General Electric Co. and Safran that makes engines for many older-generation Airbus SE A320 and Boeing 737 aircraft. 

The alert, known as an Unapproved Parts Notification, is the first formal warning to the US aviation sector over potential risks posed by thousands of spare jet-engine parts sold with forged airworthiness documentation by AOG. 

European regulators had previously warned about forged parts from the UK company. The Safran CEO said they were alerted a few weeks ago by an aircraft operator, who inquired about a part that looked to have a suspect origin. 

AOG Technics also improperly sold bushings for GE’s CF6 engine family without the jet-engine manufacturer’s approval, distributing parts with falsified documents, according to the FAA notice. The engine has been used on a number of wide-body jets, including older versions of Boeing Co.’s 747 jumbo jet.

The notice reflects a small portion of the potential fallout. Regulators and companies, including GE and Safran, have identified dozens of falsified records accompanying the sale of parts by AOG Technics. “Lessons will need to be learned” from the case, the Safran CEO said on Friday. 

“When one thinks about it, it’s a bit strange that a phantom company can be allowed to supply spare parts with false certification documents,” he said. 

Only two of those documents were forged FAA records for CF6 components, CFM has said. Meanwhile, more than 76 European Aviation Safety Agency documents linked to the sale of CFM56 parts have been falsified. The CFM56 is the world’s best-selling jet engine and powers older 737 and Airbus A320 planes. 

Most of the falsified documents are associated with commodity parts such as bushings and fasteners, a CFM spokesman said. Bushings are isolator bearings that allow engine parts to rotate without the need for lubricants.

Airlines, maintenance providers and regulators across the globe have been scouring their records to hunt down AOG-supplied parts after European authorities in August determined the parts broker had supplied the suspect components. 

American Airlines Group Inc. joined a growing number of carriers that have discovered improperly certified parts. The airline disclosed the finding to Bloomberg News late Thursday, hours after the FAA warning. The carrier didn’t immediately identify the type of parts it found. 

“Through the work of internal audits as well as collaboration with our suppliers, we’ve identified the uncertified components on a small number of aircraft — each were immediately taken out of service for replacement,” a spokeswoman for the airline said. “We’ll continue working with our suppliers and coordinating closely with the FAA to ensure these parts are no longer in our supply or otherwise in use on our aircraft.”

So far, United Airlines Holdings Inc., Southwest Airlines Co., Portugal’s TAP and Virgin Australia Airlines have also disclosed that they found engines with suspect parts.

The scandal has shaken an industry where safety is the guiding principle, with exacting standards for aircraft manufacturing and maintenance that demands each component be verified.