The results, these officials said, also indicate that during the FAA certification process for the 737 MAX, Boeing didn’t flag the automated stall-prevention feature as a system whose malfunction or failure could cause a catastrophic event. Such a designation would have led to more intense scrutiny.

FAA engineers and midlevel managers deferred to Boeing’s early safety classification, the inquiry determined, allowing company experts to conduct subsequent analyses of potential hazards with limited agency oversight. Boeing employees who served as designated agency representatives signed off on the final design, according to people familiar with the findings.

Read also: Technology versus crew – the search for answers on Boeing 737 Max crashes

Over the years, the FAA increasingly has relied on so-called authorised designees to act for the agency, with the goal of freeing up government resources to focus on what are deemed to be the most important and complex safety matters. Last year, Congress endorsed and expanded the FAA’s authority to utilise such company resources in approving new aircraft, systems and parts.

The people who described the internal report didn’t specify what information and safety data Boeing shared with the FAA during the approval process, a topic that is a major focus of various ongoing investigations. Also at issue is whether agency officials performed any assessment on their own about the system’s initial safety classification, according to aviation industry officials, pilot unions and others tracking the investigations.

The FAA’s administrative review, launched in March following the second fatal 737 MAX crash, didn’t uncover any effort by Boeing to flout certification rules or intentionally provide faulty data to the FAA, according to people familiar with the findings.

But it remains unclear what formal processes the FAA had in place to conduct an assessment independent of the initial determination by the Chicago-based company that MCAS wasn’t critical to safety and therefore didn’t warrant close FAA scrutiny.

Topics covered by the internal review are likely to come up during testimony by acting FAA chief Daniel Elwell to the House subcommittee.

The hearing is expected, among other things, to delve into FAA decisions to certify the MAX as the latest version of a decades-old design, and the extent to which computer analyses and actual flights were used to test MCAS. In recent weeks, lawmakers also have raised questions about staffing levels inside the agency, the anticipated schedule to return the jetliners to commercial service and Boeing’s failure to widely share safety details before and after the dual crashes.

The hearing comes as a Justice Department probe into the aircraft’s initial approval, previously reported by The Wall Street Journal, has broadened to include subpoenas issued to pilot unions as well as airlines. Some unions have complained about what they call Boeing’s lack of transparency as well as its shifting safety explanations of MCAS-related matters.

Boeing designed the flight-control system to rely on a single sensor to verify data about the angle of a plane’s nose. Investigators have said that in both accidents, errant data from a single sensor caused the MCAS system to strongly push down the jet’s nose, eventually causing a steep and fatal dive.

Boeing and the FAA are now working on a software fix that will feed MCAS with information simultaneously from two sensors, and immediately shut down the system if data streams significantly differ.

In its original analysis of MCAS, Boeing considered the potential for erroneous data from a single sensor, according to a person familiar with the matter. But in the end, company officials have said, Boeing determined that dual sensors weren’t required because trained pilots would know to turn off MCAS using established cockpit procedures.

That reasoning is one of the matters investigators are examining, according to people with knowledge of the probes.

Boeing’s description of MCAS came up in talks with pilot unions after the first MAX crash in October in Indonesia. In contrast to the company’s early stance that the system wasn’t deemed critical for safety, Boeing executive Mike Sinnett described it as “flight-critical software” in explaining to American Airlines pilots why a software fix shouldn’t be rushed, according to the group’s president, Capt. Dan Carey, who reviewed a recording he made of the November meeting.

A Boeing spokesman said Mr. Sinnett disagreed with Mr. Carey’s characterisation.

In describing the approval process, a Boeing spokesman has said, “The FAA considered the final configuration and operating parameters of MCAS during MAX certification and concluded that it met all certification and regulatory requirements.”

Read also: Boeing 737 Max – a perfect legal storm gathers

At the November meeting with Mr. Sinnett and other company officials, the pilots union’s safety chairman asked Boeing to push the FAA to order software fixes for 737 MAX planes. “It would have set them down,” Capt. Mike Michaelis said Tuesday of the emergency action he urged at the meeting at union headquarters in Fort Worth, Texas. His request was earlier reported by the New York Times.

Boeing said it is committed to learning from both MAX accidents and “ensuring that similar accidents never happen again.”

Previously, an FAA spokesman said the agency is determined to unravel the precise actions and sequence of events that resulted in the troubled plane’s approval in 2017. “There are several independent reviews of both Boeing and FAA processes regarding the certification of MAX and, specifically, the aircraft’s automated flight system,” the spokesman said.

In testimony to the Senate Commerce, Science and Transportation Committee two months ago, Mr. Elwell said detailed safety assessment and approval of the suspect system was “delegated,” or handed over, to Boeing relatively early in the approval process under standard procedures. But he didn’t tell senators how that initial decision was reached or exactly what role FAA officials played in subsequent safety assessments.

The FAA’s findings won’t be the definitive word on the approval process for the beleaguered MAX fleet. The US Department of Transportation, federal prosecutors and the staff of the full House Transportation and Infrastructure Committee are all looking into details of the certification, including whether Boeing misled or provided incomplete information to the FAA.

Several outside advisory groups, including one composed of eight foreign regulators, also are examining related issues surrounding certification of the 737 MAX. None of those other inquiries has yet to yield preliminary findings.

In recent days, pilot unions for the three US operators of the 737 MAX – Southwest Airlines Co., American Airlines Group Inc., and United Continental Holdings Inc. – said they received subpoenas. Former Boeing employees, including some who worked on the MAX, have also received broad subpoenas for documents related to the aircraft.

Southwest and American have also received subpoenas, representatives for the airlines said. A spokesman for United declined to comment.

Pilot unions at American and Southwest have criticized Boeing for not including details about MCAS or its potential hazards in pilot manuals or training. Southwest has said the carrier learned only after the Oct. 29 crash of a Lion Air 737 MAX that cockpit warnings related to sensors that trigger MCAS were installed on the aircraft but not working. United has said it learned after the March 10 crash of an Ethiopian Airlines jet.

For FAA critics such as Rep. Peter DeFazio, the Oregon Democrat who chairs the full Transportation and Infrastructure Committee, the agency’s internal review is likely to provide fresh ammunition for complaints that the agency generally has delegated too much authority to industry -including aircraft certification functions – often without proper safeguards. Immediately after the U.S. MAX fleet was grounded in March, Mr. Fazio questioned why MCAS was approved without informing pilots or mandating additional training. “When you create a new system that is very different and complicated in that [pilots] have to override it,” he said in an interview with the Journal, “I think there should have been specific notification and required retraining.”

Write to Andy Pasztor at [email protected], Andrew Tangel at [email protected] and Alison Sider at [email protected]