Boeing will mandate on MAX jets a previously optional cockpit warning light, which might have warned of problems that possibly played a role in the crashes of Ethiopian and Indonesian planes, two officials briefed on the matter say.
The safety feature is expected to be offered as part of a software update to the MAX fleet that was grounded in the wake of the Ethiopian Airlines crash, said the officials who asked not to be identified.
The crash 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.
Boeing did not immediately comment on the plan to make the safety feature standard, but separately said it was moving quickly to make software changes and expects the upgrade to be approved by the US Federal Aviation Administration (FAA) in the coming weeks.
But Indonesia's national carrier Garuda said on Friday that customers had lost trust in the planes and it has sent a letter to Boeing asking to cancel an order for 49 MAX 8s - the first airline to publicly confirm plans to cancel an order for the troubled aircraft.
The current order was valued at $US6 billion ($A8.4 billion) at list prices and Garuda, which currently has one MAX in its fleet, said it could switch to other Boeing models.
While a direct link between the crashes has not been proven, initial investigations show similarities and attention has focused on an automated flight-control system, MCAS (Maneuvering Characteristics Augmentation System), that came into service two years ago with the MAX.
The software is designed to prevent a loss of lift that 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.
Chicago-based Boeing will also retrofit older planes with the cockpit warning light, the officials told Reuters. The world's largest plane maker previously offered the alert, but it was not required by aviation regulators.
Boeing has said it plans to make software changes to the aircraft, but it is unclear how long it will take Boeing to refit existing MAX planes with new software or hardware.
The FAA has said installation of the new software and related training was a priority.
Randy Tinseth, Boeing's vice president of commercial marketing, said the software changes include changes in the control laws of the air plane, an update of the displays, the flight manual, as well as the training.
The company has said there was a documented procedure to handle the automated system at the heart of the problem.
The two crashes killed almost 350 people.
Since the Ethiopian crash, Boeing shares have fallen 12 per cent and $US28 billion has been wiped off its market value.
Pressure has mounted on the company from US legislators, who are also expected to question the FAA. The company also faces a criminal investigation by the US Justice Department.
Consumer advocate and former US 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.
