A mechanic who worked on Boeing Co.’s 787 aircraft alleged he observed improper manufacturing at a subcontractor for the Dreamliner program, according to a statement from attorneys representing him as a whistleblower. 

Mechanic Richard Cuevas claimed he observed “substandard manufacturing and maintenance practices” on the 787’s forward pressure bulkhead — a dome shaped piece located in the jet’s nose that’s critical to maintaining cabin pressure, according to a statement by attorneys Debra Katz and Lisa Banks. 

Cuevas estimates the alleged problems he witnessed may impact as many as a dozen planes, according to the statement. 

Boeing said in a statement that the claims were reported previously and thoroughly investigated. Analysis showed the issues raised posed no safety concerns and were addressed, the company said. 

His claims were detailed in whistleblower complaints filed with the Federal Aviation Administration and the Occupational Health and Safety Administration that were made public on June 26.

The claims are the latest in a series of allegations made by current and former workers of Boeing or its suppliers to flag concerns about the planemaker’s manufacturing and quality practices. Earlier this month, a Boeing quality inspector said the company mishandled and lost hundreds of faulty 737 Max parts.