Why the Boeing 737 Max has been grounded again

US regulators have extended the ban on the Boeing aircraft involved in two deadly crashes within five months, following the discovery of a new software problem.

On Wednesday, the US Federal Aviation Administration (FAA) said it had identified a “potential risk” during simulator testing of the 737 Max 8, but did not reveal any further details, the BBC reports. The FAA has reportedly said that Boeing must address the newly discovered issue before the aircraft can return to service.

The 737 Max 8 has been grounded worldwide since March after the second of the two fatal crashes involving the aircraft. The downings of both Lion Air flight 610 and Ethiopian Airlines flight 302 are thought to have been caused by a new anti-stall system that inadvertently reduced pilot control over the aircraft.

Subscribe to The Week

Escape your echo chamber. Get the facts behind the news, plus analysis from multiple perspectives.

SUBSCRIBE & SAVE

Sign up for The Week's Free Newsletters

From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.

From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.

Sign up

“Boeing agrees with the FAA’s decision and request, and is working on the required software to address the FAA’s request,” Boeing said in a statement this week.

The Guardian reports that the new issue “means Boeing will not conduct a certification test flight until 8 July at the earliest”, and the FAA “will spend at least two to three weeks reviewing the results before deciding whether to return the plane to service”. It did not give a specific timeline.

Can Boeing get the 737 Max 8 back in the air and restore confidence in its products?

Why is the plane grounded?

Boeing has been working on its stall-prevention system known as MCAS since the Lion Air crash in Indonesia in October 2018 and the one involving Ethiopian Airlines in March of this year.

The plane was grounded in the wake of the second crash. Preliminary reports suggested that both incidents involved a failure in Boeing’s newly-implemented Maneuvering Characteristics Augmentation System (MCAS), an anti-stall system introduced on the 737 Max 8.

The system is designed to automatically bring the nose of the aircraft down if the plane’s Angle of Attack (AOA) sensors detect that the plane is pitched too high, thereby preventing a potentially catastrophic stall in mid-air.

However, an investigation revealed that the aircraft’s AOA sensor had fed faulty information to the MCAS, causing the plane’s nose to automatically pitch down and defy pilot inputs, eventually crashing. The combined death toll of the two crashes was 346.

The 737 Max was subsequently grounded by the world’s aviation authorities in March until fixes could be made.

What is the new issue?

CNN reports that a series of simulator flights to test new software developed by Boeing revealed a new flaw, but no formal statement has been issued as to the nature of the problem.

According to sources speaking to Reuters, an FAA pilot simulation revealed that when the MCAS system was activated, it had “taken longer than expected to recover the aircraft” manually.

“It was difficult for the test pilots to recover in a matter of seconds,” the source said. “And if you can’t recover in a matter of seconds, that’s an unreasonable risk.”

However, the BBC reports that other sources claim the problem was “linked to the aircraft’s computing power and whether the processor possessed enough capacity to keep up”.

Boeing said: “We are working closely with the FAA to safely return the Max to service.”

What happens next?

“The FAA recently found a potential risk that Boeing must mitigate,” the FAA said in the statement. “The FAA will lift the aircraft’s prohibition order when we deem it is safe to do so.”

Deutsche Welle reports that Boeing was “in complete agreement with the authorities on the matter and would continue to seek a solution”.

The company said: “Boeing will not offer the 737 MAX for certification by the FAA until we have satisfied all requirements for certification of the MAX and its safe return to service.”

The BBC adds that if regulators are unsatisfied with the software fix, the “microprocessor unit will have to be replaced and the grounding may stretch on for months longer than previously thought”.

As a precaution, American Airlines, United Airlines and Southwest Airlines have all announced that they will not be using the Max as part of their fleets until at least September.