With the faith of the aviation industry and the flying public in its bestselling 737 MAX aircraft on the line, Boeing is going to brief more than 200 pilots, technical experts and regulators at its Renton facility in Washington state on Wednesday.

The plane manufacturer is going to present new software fixes for its MAX 8 and 9 planes following the Lion Air and Ethiopian Airlines crashes in which nearly 350 people were killed.

One executive from a major European airline that owns a number of MAX 8s, with more due to be delivered, has warned "the plane is a long way away from being ready" - and claimed it could be a while before it returns to the skies.

Requesting anonymity because they were not authorised to speak publicly, the executive emphasised Boeing's proposed changes need to be approved by regulators.

They told Sky News: "The MAX 8 is in the very early stages of re-entering the market and we must wait for re-certification."


Image: The aircraft has been grounded across the world

Boeing's fixes relate to the Manoeuvring Characteristics Augmentation System, known as MCAS for short.

Officials investigating last October's Lion Air crash in Indonesia have said the pilots in that incident battled without success to override MCAS, which is designed to take data from sensors measuring the plane's "angle of attack" in the air.

If MCAS understands that the angle of attack is too steep, indicating an impending stall, it automatically and repeatedly pushes the nose of the aircraft down.

In the case of Lion Air, an angle of attack sensor fed MCAS incorrect data, and it has been reported that the pilots did not seem to know how to regain control over the aircraft - desperately flipping through manuals as their plane dove downwards.

Image: Investigators examine engine parts from the Lion Air flight that crashed into the Java Sea in October

The same system is being closely scrutinised in relation to the Ethiopian Airlines crash earlier in March, amid reports the plane behaved in a similar way - plunging towards the ground shortly after take-off.

French investigators said there were "clear similarities" between the two crashes.

While there has been an initial accident report about the Lion Air incident, the Ethiopian Airlines crash investigation is still in its early stages.

Image: All 157 people on board the Ethiopian Airlines flight were killed in the crash

One pilot for a major US airline, who requested anonymity because they were not authorised to discuss the matter publicly, expressed concern that Boeing's software fix - which was designed to deal with issues raised by the Lion Air crash - is coming before the aviation industry and its regulators fully understand what happened on the Ethiopian Airlines flight.

Another said: "What if the Ethiopian incident is not MCAS? Then we're back to the drawing board."

The briefing in Renton comes as the Senate transport committee is due to question the acting head of the Federal Aviation Administration (FAA) on Capitol Hill.

Image: Part of the wreckage at the scene of the Ethiopian Airlines crash

The US department of transport has launched an independent review of the FAA's certification process after it was claimed that the regulator granted Boeing too much authority to sign off on its own designs.

Sky News understands that the changes proposed by Boeing may include measures that restrict MCAS to responding only once to a high angle of attack incident, rather than repeatedly.

Boeing may also propose the inclusion of software that will prevent MCAS responding to angle of attack data if there is significant "disagreement" between sensors collecting that data.

It is thought Boeing is considering including two additional safety features as standard rather than optional: a constant indicator of the angle of attack available on the pilot's display, and a light in the cockpit indicating when the plane's angle of attack sensors significantly disagree with one each other.

In addition, Boeing is to recommend supplemental training for pilots.

Sky News understands pilots from major US airlines have already tested out the software on simulators at a Boeing facility.

A US aviation industry source with knowledge of the testing said that pilots who took part in order to understand the MCAS changes responded "favourably" to the experience.

The individual welcomed what they called Boeing's inclusive approach to airlines and pilots as the company works to regain the trust of the aviation community in relation to the MAX aircraft.

But American Airlines pilot union spokesperson and MAX 8 pilot captain Jason Goldberg told Sky News that the manufacturer would need to work extremely hard to restore faith after failing to flag the MCAS system to pilots when the plane was first released.

Mr Goldberg called that "inexcusable" and a "betrayal of trust".

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A Boeing spokesperson said: "Listening to pilots is an important aspect of our work. Their experienced input is front and centre in our mind when we develop aeroplanes.

"We share a common priority - safety - and we listen carefully to their feedback to make sure we are always focused on how to improve what is already the safest way to travel."

Sky News has made numerous requests for an on camera interview with a representative from Boeing, but Boeing has refused.