WASHINGTON/JAKARTA (Reuters) - Boeing Co plans to offer as standard a safety feature that might have warned earlier of problems that possibly played a role in the crashes of Ethiopian and Indonesian planes that killed almost 350 people, two officials briefed on the matter said on Thursday.

Boeing will mandate a previously optional cockpit warning light as part of a software update to the 737 MAX fleet that was grounded in the wake of the fatal crashes, said the officials, who asked not to be identified.

The March 10 Ethiopian Airlines crash that killed all 157 on board has set off one of the widest inquiries in aviation history and cast a shadow over the Boeing MAX model intended to be a standard for decades.

Initial investigations show similarities between the Ethiopian crash and the Indonesian accident in October that killed all 189 crew and passengers. A direct link between the crashes has not been proven, but attention has focused on an automated flight-control system, MCAS (Maneuvering Characteristics Augmentation System), that came into service two years ago with the MAX.

Chicago-based Boeing, which the officials said also will retrofit older planes with the cockpit warning light, previously offered the alert, but it was not required by aviation regulators.

It is unclear how long it will take Boeing to refit existing MAX planes with new software or hardware. Experts said it could take weeks or months to be done, and for regulators to review and approve the changes. Regulators in Europe and Canada have said they will conduct their own reviews of any new systems.

The software is designed to prevent a loss of lift which can cause an aerodynamic stall, sending the plane downwards in an uncontrolled way. In the Lion Air crash, it may have been erroneously activated by a faulty sensor, investigators believe. The FAA has said installation of the new software and related training was a priority.

STEPS TO IMPROVE SAFETY

Boeing did not immediately comment on the plan to make the safety feature standard.

However, in London Thursday, Randy Tinseth, Boeing’s vice president of commercial marketing, said the manufacturer is moving quickly to make software changes and expects the upgrade will be approved by the U.S. Federal Aviation Administration (FAA) in the coming weeks.

“That includes changes in the control laws of the airplane, an update of the displays, the flight manual, as well as the training,” he said at a conference, adding Boeing has tested the improvements in a simulator and in the air.

The product and training updates were being made “to further improve the safety that ensures that this will not happen again,” Tinseth said.

He said it was too early to speculate on what the investigations will show, but defended Boeing’s design and production processes.

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Boeing also said it would slow work at its 737 plant in Seattle next week to allow employees to catch up on work that was previously delayed, but said this was because of winter storms and supplier delays and not fallout from the crashes.

Meanwhile, in Jakarta, Indonesian investigators described the panic of pilots grappling with airspeed and altitude problems in the last moments of the Lion Air flight.

“It seemed the pilot felt he could no longer recover the flight. Then the panic emerged,” Nurcahyo Utomo, an investigator at Indonesia’s national transportation committee, said.

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Reuters reported Wednesday the Lion Air pilots scrambled through a handbook to understand why the jet was lurching downwards in the final minutes before it hit the water.

A final report on the Lion Air crash is expected in August.

Boeing has said there was a documented procedure to handle the automated system at the heart of the problem.

In both flights, crews radioed about control problems shortly after take-off and sought to turn back.

MULTIPLE INQUIRIES

Investigations of Boeing’s conduct are starting to pile up, with several lawsuits already filed on behalf of victims of the Lion Air crash referring to the Ethiopian accident. Boeing declined to comment on the lawsuits.

Consumer advocate and former U.S. presidential candidate Ralph Nader lost a grand-niece in the Ethiopian crash and urged whistleblowers to help challenge the aviation industry and get to the bottom of what happened.

“They lulled us into complacency,” he said in an interview in Thursday’s Wall Street Journal.

SIMULATORS

Simulators for the MAX are now being manufactured but they have yet to be delivered to most airlines that have ordered them. Ethiopian Airlines said on Thursday the simulators are not designed to replicate the MCAS problems.

The airline is among the few that do have such a simulator but the captain of the doomed flight had no chance to practice on it before the fatal crash, a pilot colleague said.

In Washington, Boeing faces a criminal investigation by the U.S. Justice Department and executives also will be summoned to a U.S. Senate panel hearing for questioning.