Boeing recently found improperly torqued bolts in several areas of new-build 737 Max jets, indicating a quality problem similar to that revealed by the Federal Aviation Administration (FAA) on 23 March.

A source familiar with the matter says that earlier this year Boeing discovered improperly torqued bolts on 737 landing gears and wing ribs.

Boeing says the torque finding does not reflect a systemic issue and that its discovery of mis-torqued bolts reflects its regular process of ensuring production quality.

The source, who asked not to be identified due to the sensitive nature of the issue, says the company uncovered the problems through internal audits of its 737 assembly site in Renton.

A 737 Max wing tip in Boeing's Renton production site on 15 June 2022

Source: The Seattle Times, Ellen Banner, pool reports

Boeing discovered bolt-torque problem after an audit of its Renton production site

Boeing reported the findings to the FAA and stepped up its own internal quality oversight to address the issue.

Under its previous procedures, Boeing allowed some assembly workers to self-certify they had applied the specified torqued when tightening certain bolts. Workers did so by making notes of torque readings and of the tools they used.

But in response to its audit, Boeing on 13 February added another layer of oversight by requiring “witness inspections”, the source says. That means designated quality assurance employees visually confirm torque readings.

Boeing says such “witness inspections” are implemented from time to time and are a standard means of ensuring quality.

“Boeing continuously focuses on delivering high-quality products that meet all regulatory requirements,” it says. “We work transparently with the Federal Aviation Administration to address issues if and when they arise.”

The source adds that in late February inspectors from the FAA spent several days at the Renton 737 assembly site.

Boeing maintains the visit was pre-scheduled and did not uncover torque issues.

But the FAA declines to comment specifically on the reason for its visit. “The FAA is providing the routine oversight of Boeing’s production quality system, which involves scheduled and unscheduled audits and other oversight activities,” the agency tells FlightGlobal.

Another Boeing torque issue came to light on 23 March when the FAA released an airworthiness directive applying to 330 US-registered 737 Max aircraft – essentially the entire US fleet of the type.

A 737 Max CFM Leap engine in Boeing's Renton assembly site

Source: The Seattle Times, Ellen Banner, pool reports

The anti-ice exhaust ducts are found at the bottom of Leap-1B turbofans on the 737 Max

That AD specifically addresses improperly torqued bolts that hold down anti-ice exhaust ducts found on the bottom of the aircraft’s CFM International Leap-1B turbofans.

Boeing assembles the Max’s nacelle inlets at its propulsion facility in North Charleston, South Carolina, although it is not clear where the mis-tourquing occured. 

Boeing insists no relationship exists between the two bolt-torque issues.

Pilots had “discovered a bolt protruding through a drain hole at the bottom of the engine inlet”, near the engine anti-ice exhaust vent, says the FAA’s AD.

“Boeing determined that some of the fasteners for [engine anti-ice] exhaust ducts were installed at the factory with inadequate torque due to the use of a prohibited yoke-style torque wrench adapter,” the FAA’s AD adds. “When used at a sufficiently large angle… this adapter will produce a significant under-torque of the installed fasteners.”

Those exhaust ducts compose a system that sends hot air into the engine’s inlet to prevent ice formation. Over time, loose fasteners could allow heated air to hit and damage the engine’s composite inner barrel structure, possibly causing engine failure, the FAA says.

The FAA order affects 737 Max 8s, Max 8-200s and Max 9 variants.

The agency declines to comment about torque issues involving any other 737 Max components.