A fix to the anti-stall system suspected in the crash of a Boeing 737 MAX 8 jet that killed 189 people in Indonesia is ready, industry sources said Saturday, as the company tries to avoid a lengthy grounding of its planes.

Boeing was due to present the patch to officials and pilots of US airlines American, Southwest and United in Renton, Washington state, where the plane is assembled, other sources said.

The Lion Air crash in Indonesia last October and another accident this month involving an Ethiopian Airlines jet, which killed 346 people between them, have raised major concerns about the safety certification of the 737 MAX 8 model.

Although it will take months to determine the exact cause of both crashes, investigators in the Lion case have honed in on the MCAS automated anti-stalling system designed to point the nose of the plane downward if it is in danger of stalling, or losing lift.

The FAA had given until April for Boeing to make the necessary changes to the critical anti-stall system, and on March 15 two anonymous industry sources told AFP the upgrade would be ready in about 10 days.A spokesman for United Airlines, whose fleet includes 14 of the 737 MAX 9 planes, confirmed the company’s attendance at the training session.

Southwest and its SWAPA pilots union “have subject matter experts from our Technical Pilot Team and Training Teams headed to Boeing to review documentation and training associated with the modification to the B737 speed trim system,” a spokeswoman said.

“We’ve been working diligently and in close cooperation with the FAA on the software update. We are taking a comprehensive and careful approach to design, develop and test the software that will ultimately lead to certification,” a Boeing spokeswoman said.

“There will be training provided by Boeing.” In addition to the software modification, the industry sources said Boeing has also finalized updates to its flight and pilots’ training manuals, as the FAA asked.

“We have been engaging with all 737 MAX operators and we are continuing to schedule meetings to share information about our plans for supporting the 737 MAX fleet,” the Boeing spokeswoman said, declining to confirm the timeline for the changes.

In another modification, the 737 MAX will be outfitted with a warning light for malfunctions in the anti-stall system, an industry source told AFP on Thursday, standardizing a feature previously sold as an optional extra.

Share value of the firm, which says it is the world’s largest aerospace manufacturer, has dropped 12 percent since the accident, wiping out $28 billion in market capitalization Boeing and the FAA are under investigation by the Transportation Department over how the rollout of the jet was handled, including the anti-stall system.The acting FAA head is among transport officials who are to testify on Wednesday before a congressional subcommittee.

Questioning is likely to focus on tight links between Boeing and the regulators, who maintain offices in the airplane factories and delegated a large part of the certification process for the 737 MAX and its anti-stall system to employees of Boeing, sources said.