Boeing says it has completed the software update for an anti-stall feature on the 737 MAX and is working with the United States Federal Aviation Administration (FAA) towards a certification test flight.
But Boeing's announcement - which lifted shares of the embattled company - comes only a week before the US Federal Aviation Administration is set to brief its worldwide peers among civil aviation regulators on its process for allowing the planes to fly again.
"Boeing did not treat the 737 Max 8 situation like the emergency it was", said Daniel Carey, president of the American Airlines pilots' union, which has filed public records related to the matter.
"With safety as our clear priority, we have completed all of the engineering test flights for the software update and are preparing for the final certification flight", said Boeing CEO Dennis Muilenburg.
USA officials said American Airlines, Southwest Airlines and United Airlines flew tens of thousands of flights with the MAX and reported no unusual incidents with MCAS.
In those accidents, erroneous readings from a single sensor triggered software known as MCAS, which pushed down the nose of each aircraft until pilots lost control. The safety of the aircraft has come under intense scrutiny in the wake of two crashes taking the lives of all 346 people on board.
"Boeing has developed enhanced training and education materials that are now being reviewed with the FAA, global regulators, and airline customers to support return-to-service and longer-term operations", the company statement said.
But the only orders reported by Boeing for April were bookkeeping entries: Four 737 Max jets that had been sold to Boeing Capital in the past were transferred to an unidentified lessor last month.
After the first crash, of a Lion Air jet, Boeing told USA pilots at the end of November that it could have the software fix ready in about six weeks.
Other reports have indicated flight crews may not have been aware the systems were not operational by default or otherwise received insufficient training.
"I would call it the beta version", Lawrence said. On May 23, the FAA is due to convene a meeting in Texas to review the preparations for a return to service, and Boeing indicated that similar conferences would be conducted in other locales. "We don't know what training is like for Lion Air pilots or Ethiopian pilots". When both Boeing and the FAA refused to ground the aircraft, the world's airlines and aviation authorities took things into their own hands.