Houston ? The company whose drilling triggered the Gulf of Mexico oil spill also owns a rig that operated with incomplete and inaccurate engineering documents, which one official warned could “lead to catastrophic operator error,” records and interviews show.

In February, two months before the Deepwater Horizon spill, 19 members of Congress called on the agency that oversees offshore oil drilling to investigate a whistle-blower’s complaints about the BP-owned Atlantis, which is stationed in 7,070 feet of water more than 150 miles south of New Orleans.

The Associated Press has learned that an independent firm hired by BP substantiated the complaints in 2009 and found that the giant petroleum company was violating its own policies by not having completed engineering documents on board the Atlantis when it began operating in 2007.

Stanley Sporkin, a former federal judge whose firm served as BP’s ombudsman, said that the allegation “was substantiated, and that’s it.” The firm was hired by BP in 2006 to act as an independent office to receive and investigate employee complaints.

Engineering documents — covering everything from safety shutdown systems to blowout preventers — are meant to be roadmaps for safely starting and halting production on the huge offshore platform.

Running an oil rig with flawed and missing documentation is like cooking a dinner without a complete recipe, said University of California, Berkeley engineering professor Robert Bea, an oil pipeline expert who has been reviewing the whistle-blower allegations and studied the Gulf blowout.

“This is symptomatic of a sick system. This kind of sloppiness is what leads to disasters,” he said. “The sloppiness on the industry side and on the government side. It’s a shared problem.”