Dish Soap to Help Build Planes? Boeing Signs Off on Supplier’s Method.

A recent Federal Aviation Administration audit of the production of the Boeing 737 Max raised a peculiar question. Was it really appropriate for one of the plane maker’s key suppliers to be using Dawn dish soap and a hotel key card as part of its manufacturing process?

The answer, it turns out, may be yes.

The F.A.A. conducted the audit after a panel known as a door plug blew off a 737 Max 9 during an Alaska Airlines flight in January. The New York Times reported last month that the agency’s examination had identified dozens of problems at Boeing and the supplier, Spirit AeroSystems, which makes the fuselage of the 737 Max.

Boeing and Spirit have both come under intense scrutiny after the episode involving the Alaska plane, which appears to have left Boeing’s factory in Renton, Wash., missing four bolts used to secure the door plug in place. Spirit has had its own share of quality problems in recent years and has been bruised by financial losses, and Boeing said last month that it was in talks to acquire the company, which it spun out in 2005.

But in the aftermath of the Alaska episode, Spirit says one thing has been misunderstood: its use of the dish soap and the hotel key card.

In fact, the company says it is now properly authorized to use the soap as well as a newly created tool that resembles a key card. Both have been approved by the appropriate engineering authorities at Boeing and documented for use under F.A.A. standards as factory tools known as shop aids, according to Spirit.

“People look at the hotel key card or Dawn soap and think this is sloppy,” said Joe Buccino, a Spirit spokesman. “This is actually an innovative approach to solving for an efficient shop aid.”

A Boeing spokeswoman confirmed that the company had approved the use of the soap and the key card tool as shop aids. The F.A.A. said it could not comment because the audit was part of its continuing investigation in response to the Alaska episode.

As part of the audit, agency employees visited Spirit’s factory in Wichita, Kan. One aspect of the manufacturing process they scrutinized was how Spirit handled door plugs, which take the place of emergency exits that would be needed if a plane was configured with a denser seating arrangement.

At one point, the F.A.A. observed Spirit mechanics using a hotel key card to check a door seal, which was “not identified/documented/called-out in the production order,” according to a document describing some of the audit findings.

Spirit officials said the key card was used to check the gap between the seal and the door plug to make sure there was no obstruction, rolling or pinching. Workers had previously tried other tools that either were too brittle or did not bend enough. But Spirit engineers found that the key card, with rounded corners and just the right amount of flexibility, allowed them to check the gap without damaging the seal.

After Spirit workers were spotted using the key card, the company’s engineers developed a similar tool for its employees to use moving forward. The new device, which is green and square, is meant to be a scraping tool, but Spirit smoothed its serrated edges and rounded its corners.

Sean Black, Spirit’s chief technology officer, led the effort to get the new tool approved for use by Boeing and properly documented.

“Our workers routinely find creative ways to make the process of building fuselages more efficient,” Mr. Black said. “In this case, workers created the door rigger seal tool, which allows our teams to test the door seals without any risk of degrading the seal over time.”

Then there was the matter of the dish soap.

At another point during the audit, the F.A.A. saw Spirit mechanics apply liquid Dawn soap to a door seal “as lubricant in the fit-up process,” the document describing some of the audit findings said. The agency also saw the door seal get cleaned with a wet cheesecloth to remove the soap and debris, according to the document, which said that instructions were “vague and unclear on what specifications/actions are to be followed or recorded by the mechanic.”

Those observations dealt with the process in which workers make sure the seal is properly installed against the door frame. Mr. Buccino said the Dawn soap was to ensure there were not tears or bulging when the seal was being installed. He said the chemical properties of the soap were found not to degrade the resilience of the seal over time. Spirit again worked to get Boeing’s approval to use the soap and to get it properly documented.

Spirit workers did not land on the dish soap on the first try. Mr. Buccino said that other common products had been used in the past — including Vaseline, cornstarch and talcum powder — but that they ran the risk of degrading the seal over time.