Airlines have been on the lookout for potentially dodgy spare parts.
The supplier has been under investigation by regulators who say it used false documentation.
United, Southwest, and Virgin Australia have all identified suspect parts, per Bloomberg.
United Airlines has joined the ranks of air carriers affected by inauthentic engine parts from a supplier called AOG Technics, Bloomberg first reported.
The European Union Aviation Safety Agency issued a notification about the London-based supplier last month, suspecting unapproved parts.
It said AOG Technics had used false documentation for engine parts of unknown origin.
Bloomberg previously reported the dubious parts were used for repairs of CFM56 engines, which power many Airbus A320 and Boeing 737 planes, leaving companies scouring their records for references to the supplier. The total number of suspect spare parts is still unknown.
Since then, three major airlines have discovered that the components had been used in some of their engines.
A spokesperson for United told Insider that components were discovered in a single engine on each of two aircraft, one of which was already undergoing routine maintenance.
"We are replacing the affected engines on both aircraft before they are returned to service, and we'll continue to investigate as new information becomes available from our suppliers," they added.
Also on Monday, Virgin Australia Airlines found a second suspected unapproved part from AOG Technics, Bloomberg reported. Flightradar24 data showed the Boeing 737 in question was diverted during a flight on Saturday.
"At Virgin Australia, safety is our highest priority and we apply a highly stringent approach to maintenance to ensure our safety standard is upheld," a spokesperson told Insider.
Southwest Airlines was the first major carrier to disclose that it had identified components from AOG Technics. "We became aware of the issue in early August and took necessary steps to ensure we do not have any parts in our fleet from AOG," a spokesperson said in a statement shared with Insider.
"Our suppliers conducted a review of Southwest parts and identified one engine that contained two low-pressure turbine blades from this vendor. In an abundance of caution, we made an immediate decision to promptly replace those parts on that single engine."
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