Report raises new questions about structural integrity of Boeing 787 Dreamliner

As Boeing struggles to regain altitude after its high profile difficulties with the grounding of its 737 Max and the coronavirus pandemic, new documents obtained exclusively by KOMO News Radio show the company could be be facing new questions about the structural integrity of its Boeing 787 Dreamliner, this time involving the vertical tail fin on that aircraft.

A review of the records show that engineers raised concerns about the vertical tail fin on the jetliner, concerns that were first voiced six months ago.

The questions could prompt new uncertainty about Boeing's Dreamliner, which the company desperately needs to be successful.

In a statement, a Boeing spokesperson said the company is aware of the concerns.

"We continually assess potential manufacturing and safety issues," the statement said. "This issue was found in late 2019 and has already been addressed in production."

Mechanical review

It started with a mechanic.

It's not clear what airline the the mechanic worked for, but the technician noticed something wrong on a Boeing 787 Dreamliner while working on the tail of the aircraft. The mechanic noticed a slight dimple, also known as a depression, on the vertical fin, near the spot where it joins with the aircraft's fuselage.

While a tiny dent or ding isn’t a problem on a car or SUV, they’re not too common on a multi-million dollar passenger jet. The mechanic reported the issue, prompting federal investigators to scrutinize nearly every plane in the entire Dreamliner fleet, according to documentation examined by KOMO News Radio.

Late last month, Boeing acknowledged that eight Dreamliners had been grounded because of issues with structural defects . Earlier this week, a company spokesperson acknowledged that Boeing is also reviewing an issue involving the structure of the plane on the horizontal stabilizer.

KOMO News has now learned that there are safety concerns about the vertical tail fin of the plane as well, a concern that was first raised in March.

One federal document focuses on issues with shims.

When a plane is assembled, pieces must be put together and connected within hundredths of an inch. There are frequently microscopic gaps, which are filled in using a part known as a shim.

"This depression was located at a joint common to the Main Torque Box (MTB) skin, Rear Spar, and Route Fitting #4. Shims were properly installed prior to drilling of holes," an investigator wrote. "Investigation suggests these shims were later discarded before final fastener installation. Measurement on aircraft prior to rework show un-shimmed gaps up to 0.034.”

In ordinary construction, or on the body of a car, 0.034 inches is almost unnoticeable but planes are quite different.

The FAA document indicates inspectors worry that the gap could lead to an unsafe condition on a Dreamliner.

“The excessive gap produced a greater than design preload in the affected details,” the report found. “The increased preload combined with the design loads could exceed the limit load capability of the joint.”

The limit load on a plane is the maximum weight allowed in a normal flight. Anything more than the limit load could cause strain on the structure of the plane, and over time, that strain can lead to serious issues if left unaddressed, experts say.

The federal document outlines what many engineers say is a worst-case and unlikely scenario, but not impossible: “The condition could result in failure of a PSE (principal structural element) to sustain limit load and could adversely affect the structural integrity of the airplane and result in loss of control of the airplane.”

A retired Boeing engineer who requested anonymity in order to speak freely notes the importance of PSE in aerospace.

“It’s any piece of structure on an airplane whose failure would result in a catastrophic event.”

The statement from the Boeing spokesperson suggests otherwise.

"Our engineers conducted a thorough analysis and found it did not immediately affect the safety of flight and no immediate action is required," the Boeing spokesperson said. "We are working with the FAA to finalize guidance for the in-service fleet. Our expectation is that this will require a one-time inspection during regularly scheduled maintenance. "

Now federal investigators are trying to figure out how many planes have a similar issue.

Every individual 787 is given a unique identification number, known as a line number, or LN.

The LN’s start at number 1 and go up from there.

“The affected LNs extend to LN 6-687,” the report says, which represents 681 total planes. "689-873, 875-885, 889-890, 895, 896, & 897.”

Based on what the report found, that represents hundreds of planes or the vast majority of the Dreamliner fleet that could contain issues with its vertical tail fin.

Investigators say the issue was document at planes assembled in both Boeing Dreamliner facilities in Everett and Charleston, S.C.

“Capture and control investigation showed this depression could be present on both sides (LHS and RHS) and from both manufacturing facilities,” the document said.

The focus of their concern appears to be with final assembly of the plane.

For some reason, workers removed shims that were in place before the final installation of fasteners.

It appears those shims were supposed to remain, but were instead discarded. Inspectors now want to know why that happened, and what the long-term effects of the missing shims could be.

"The increased preload could also reduce the life of the details or induce damage/delamination to where the baseline maintenance inspection program is no longer adequate,” investigators wrote.

One possible remedy for the issue could be increased inspections of planes.

“You always want to avoid any gaps,” the retired Boeing engineer told KOMO News. “That’s what they use shims for. Because otherwise, you’re just going to pre-load. You’re going to crank it. The fact that you have dimples, that’s very indicative that you’ve got pull-up in the fasteners.”

When asked about seeing a dimple at that joint, he said, “That doesn’t make a whole lot of sense to me.”

The engineer said he believes this is an issue that can be addressed by engineers and can be fixed, but that it cannot be ignored.

He said that will likely be the next order from the FAA.

He says inspectors will want to know if there’s anything that can be observed or measured in the affected planes, using different kinds of equipment.

“Depending on the findings, then you have different engineering instructions on how to fix it,” he said. “There’s no standard ‘ground it until it’s fixed."

When contacted by KOMO for comment on this story about the vertical fin, a FAA spokesperson referred to a statement earlier this week about issues found near the horizontal stabilizer.

“The Federal Aviation Administration is investigating manufacturing flaws affecting certain Boeing 787 jetliners. The agency continues to engage with Boeing. It is too early to speculate about the nature or extent of any proposed Airworthiness Directives that might arise from the agency’s investigation.”

When asked about this latest discovery, the spokesperson emphasized “Our statement from Monday will still hold. We are looking into flaws, plural.”