New report reveals why Boeing’s 737 Max has taken so long to return to service

The cockpit of a Boeing 737 Max 8 in June 2018.

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The cockpit of a Boeing 737 Max 8 in June 2018.
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REUTERS/Abhirup Roy

  • A near crash during a flight-simulator session in June led to a redesign of the Boeing 737 Max’s flight-computer architecture, according to a new Bloomberg report.
  • That redesign is in addition to the software fix to an automated system linked to two fatal crashes. It has led to extensive delays getting the plane back into commercial service.
  • The flight computer in the 737 Max, based on an older version of the 737, is now considered antiquated. The redesign brings the computer up to modern standards, better able to manage various automated systems.
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A near crash in a simulated flight in June using the software fix Boeing designed for the 737 Max led to the extensive delay that has kept the plane grounded for months, according to a new Bloomberg report.

Following the March crash of Ethiopian Airlines Flight 302, the second fatal crash involving a 737 Max in five months, Boeing engineers began designing a software fix to prevent an automated flight-control system from erroneously activating. The plane type was grounded worldwide within two days of the crash.

Initially, Boeing said it would be able to develop and implement the fix to the automated system, known as MCAS, or the Maneuvering Characteristics Augmentation System, within weeks. It later revised that to several months in order to fully test and certify the new software.

But in June, as engineers were almost finished designing the fix, several Boeing pilots got into a flight simulator to test “a few things,” Bloomberg said. A simulated computer glitch caused the plane to point its nose down, diving aggressively like the planes in both crashes.

The outcome of that simulator flight, a decision to redesign the 737 Max’s flight-computer architecture, led to extensive delays that have dragged on through the summer and fall and now threaten Boeing’s ability to deliver aircraft, book new orders, and maintain revenue expectations.

The extensive redesign – in addition to taking engineers longer – has also led to delays getting clearance from regulators, who are now looking more closely at the changes. Earlier this week, regulators demanded additional documentation from Boeing on the updates.

While the fix originally focused on MCAS, there was closer scrutiny of the entire plane following the second crash, including of how pilots would respond to multiple cockpit alarms and what would happen in both common and extremely remote emergency scenarios.

In the test that led to the computer redesign, Bloomberg reported, Boeing tested what would happen if gamma rays from space corrupted data in the plane’s flight-control system – an extraordinarily unlikely scenario, but one that must be addressed to prove to safety regulators that the plane can survive virtually any possible failure.

In the test, the plane dived toward the ground, and one of the test pilots found it difficult to respond to the various alarms and system failures in time to control the plane.

While the 737 Max previously had two computers doing separate things – one operated flight systems, and one stood by in case the first failed – the redesign has both set to monitor each other. The original setup was relatively antiquated, borrowed from older generations of the 737, and the change is more in line with modern flight design.

American civil aviation and Boeing investigators search through the debris at the site of the Ethiopian Airlines crash in March.

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American civil aviation and Boeing investigators search through the debris at the site of the Ethiopian Airlines crash in March.
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REUTERS/Baz Ratner/File Photo

MCAS and the 2 crashes

Investigations into the two crashes suggest that the MCAS erroneously engaged, forcing the planes’ noses to point down, and that pilots were unable to regain control of the aircraft. The two crashes, Lion Air Flight 610 and Ethiopian Airlines Flight 302, killed a total of 346 people.

Before the software fix, the MCAS could be activated by a single sensor reading. In both crashes, the sensors are thought to have failed, sending wrong data to the flight computer and, without a redundant check in place, triggering the automated system.

MCAS was designed to compensate for the 737 Max having larger engines than previous 737 generations, something that could cause the plane’s nose to tip upward and lead to a stall. In that situation, the system could automatically point the nose down to negate the effect of the engine size.

Boeing is aiming to submit the proposed fix – and the computer redesign – to the Federal Aviation Administration and get the plane certified to fly again by the end of 2019. US airlines have pulled the jet from their schedules until at least January.