An anti-stall system at the centre of a probe into the crash of a Boeing 737 MAX jetliner in Indonesia five months ago was also at play when the same aircraft model crashed in Ethiopia earlier this month, according to three people briefed on the matter.

Key points: Data pulled from the flight recorder suggests the anti-stall system pushed the nose of the jet downwards

Data pulled from the flight recorder suggests the anti-stall system pushed the nose of the jet downwards An Ethiopian-led investigation is trying to establish whether the system overpowered the pilots

An Ethiopian-led investigation is trying to establish whether the system overpowered the pilots Boeing and US regulators have declined to comment on the data

Data pulled from the Ethiopian Airlines flight recorder suggests the anti-stall system, known as MCAS (Manoeuvring Characteristics Augmentation System), which pushes the nose of the jet downwards, had been activated before the jet ploughed into a field outside Addis Ababa on March 10, the sources said.

The sources spoke to Reuters on condition of anonymity ahead of an interim official report.

Boeing and the Federal Aviation Administration declined to comment on the data, which was first reported by the Wall Street Journal.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 54 seconds 54 s The 737 MAX was one of Boeing's most popular jets.

It is the second related piece of evidence to emerge from the black boxes of Ethiopian flight 302 after an initial sample of data recovered by investigators in Paris 11 days ago suggested similar "angle of attack" readings to the first crash.

These initial airflow readings from the Ethiopian jet refer to stall-related information needed to trigger the automated nose-down MCAS system.

The system is designed to be activated only when the angle of attack — measuring the way the wing cuts through the air — has become too high to avoid the plane stalling or losing lift.

However, it was not immediately clear whether the system on the Ethiopian jet was responding to faulty sensor data, as in the case of the earlier crash, or genuine stall indications.

Ethiopian, French and US officials have said there are similarities between the two accidents, which led to the worldwide grounding of the recently introduced 737 MAX.

All 157 people onboard were killed when the Ethiopian Airlines 737 Max crashed. ( AP: Mulugeta Ayene )

An Ethiopian-led investigation is trying to establish whether the system overpowered the pilots, a leading scenario in the Lion Air crash, and what action was taken by the crew.

Boeing suggested using two existing cut-out switches could have prevented the Lion Air disaster, but it has also announced proposals to beef up the system and improve training.

Two of the people briefed on the matter said they presumed that the Ethiopian Airlines pilots did not hit the cut-out switches based on the airplane's speed and fatal descent, but could not confirm that the data established that.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 54 seconds 54 s The fatal Ethiopian Airlines crash has seen Boeing's 737 MAX planes grounded worldwide. (Photo: AP)

Boeing working to fix anti-stall system before US summer

Boeing is facing mounting pressure to roll out a software update to fix anti-stall technology on the Boeing 737 Max in time for airlines to use the jets during the northern hemisphere's peak summer travel season.

Company engineers and test pilots are working to fix the anti-stall technology on the Boeing 737 Max as the company's best-selling plane remains grounded worldwide and airlines are losing money by cancelling flights.

Southwest, the largest operator of the Max with 34 of them and another 249 on order, said this week that the grounding caused it to cancel 2,800 flights so far, or 30 per cent of all cancellations in the first quarter.

Southwest Airlines has grounded its Boeing 737 MAX 8 planes. ( Reuters: Mike Blake )

It said cancelled flights, including those not related to the Max, will cost it $US150 million ($211 million) in revenue for the quarter and cut its planned capacity growth for the entire year.

German tour operator TUI Group said its 2019 profit will drop about 200 million euros ($317 million) because of the Max grounding. That forecast assumes the planes are flying again no later than mid-July.

United Airlines, which has 14 Max jets, said the grounding isn't hurting the airline yet, but the financial pain "is expected to increase if the grounding extends into the peak summer travel season".

Boeing is also seeing its own expenses rise, although it would not disclose how much it is costing the company to make the software fix and also train pilots how to use it.

Cowen Research analysts say a "very rough guess" is that Boeing will pay about $US2 billion after insurance to fix the plane, pay crash victims' families and compensate airlines that had to cancel flights.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 40 seconds 40 s US aviation authorities explained the data that prompted the grounding of 737 MAX jets.

Most Wall Street analysts are betting that the planes will be flying again in less than three months, while noting that it could take longer in countries that plan to conduct their own reviews of Boeing's upgrade instead of taking the word of the US regulator, the Federal Aviation Administration.

Boeing has stopped Max deliveries during the grounding, which cuts into cash flow — Boeing gets most of its money for a plane upon delivery.

It is difficult and unusual for airlines to switch an order from one aircraft manufacturer to another. Boeing and European rival Airbus form a duopoly that dominates commercial airplane sales. Airlines considering switching from the Max to the comparable Airbus model, called the neo for new engine option, would fall to the back of a years-long backlog line.

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