Southwest, American Airlines and United have all found dodgy parts installed in their planes. The problem has been traced to a mysterious UK seller now facing a lawsuit.

• Three US airlines found illegitimate parts in their planes from AOG Technics, a UK-based company.
• The FAA said the company sold parts with unapproved paperwork — a safety hazard.

Southwest made a startling discovery earlier this month.

The airline found inside one of their planes some parts that shouldn't be there. It wasn't long before they realized they were one more victim of a much larger conspiracy.

The parts they found came from AOG Technics, a company founded in 2015 that sold parts like engine components and turbine blades. The Federal Aviation Administration discovered earlier this month that AGO Technics had sold parts with falsified paperwork to an airplane maintenance company. And the EU Aviation Safety Agency warned that "suspected unapproved parts" were coming from AOG Technics.

Not having proper approval from these agencies means they can't guarantee their quality, a worrying development for the airlines using them.

Not long after Southwest made its discovery, United made its own, announcing on September 18 that they had also identified parts from AOG Technics in their planes. On Thursday night, American Airlines said they, too, had found the illegitimate parts in some of their aircraft, Bloomberg reported.

A spokesperson for United told Insider they found the AOG Technics parts on one of the engines in two different aircraft, which they plan to replace. Meanwhile, a spokesperson for Southwest said they identified two parts on a single engine that have now been replaced. A spokesperson for American Airlines told Fortune they found the parts on only a small number of planes.

But across the world, the parts have so far been found in about 100 planes, Fortune reported.

Jet engine maker CFM International — which found several AOG Technics parts in engines it repaired — is now suing them in London for access to documents linked to parts used in certain engines since 2015, Reuters reported.

An attorney for CFM International told Reuters that AOG Technics had created a "deliberate, dishonest, and sophisticated scheme to deceive the market with falsified documents on an industrial scale."

For its part, AOG Technics seems to have closed up shop. Its website and LinkedIn page are no longer available, and Google lists the company as "permanently closed." Those running AOG Technics may have also forged fake LinkedIn profiles for made-up employees, according to Bloomberg.

AOG Technics did not respond to an emailed request for comment from Insider.