Is the 737 MAX’s Return Imminent?

Two separate crashes within five months led the latest generation of the world’s most successful commercial airliner to be grounded. As Boeing begins a pivotal week of flight safety tests, Thomas Haynes analyses the details of a saga that has lasted nearly 500 days already

The day of March 13, 2019 was a day to remember. It was the beginning of what is now the longest commercial aircraft grounding in history. But this week, a crucial set of test flights are due to take place. On June 29, a 737 MAX 7 outfitted with test equipment will depart Boeing Field near Seattle to conduct scripted mid-air scenarios.

The Boeing 737 MAX is the manufacturer's best-selling aircraft of all-time. Boeing

The purpose of the flights will be to evaluate the changes the manufacturer has made to the automated flight control system. It is thought that pilots will also trigger the Manoeuvring Characteristics Augmentation System (MCAS)
software which faulted in both crashes.

As this timeline reveals, the events of this week are the latest in a series that have spanned nearly 500 days since the type’s grounding…


March 13

Following the second crash, the US Federal Aviation Administration (FAA) bowed to mounting pressure from fellow regulators and grounded the aircraft type globally.

At this point, Boeing remained confident that the recertification effort would be completed in a matter of months.

March 27

Two weeks after the grounding, Boeing unveiled a software update designed to avoid MCAS errors. The airframer briefed more than 200 airline pilots, technical specialists and regulators at a meeting in Renton, Washington.

At the time of when the worldwide grounding was implemented, 387 aircraft were in service with 59 airlines. Boeing

The updates included changes to MCAS and specifically the angle of attack sensors. It was widely reported that if the sensors disagree by more than 5.5 degrees with the flaps retracted, then the system will not activate.

On this date, Boeing said it had already developed and tested in-flight the changes, and that it was only awaiting the FAA signoff.

April 5

To accommodate the pause in MAX deliveries, Boeing decided to slow the rate of production from 52 airframes per month to 42 starting in mid-April 2019.

At the time, Dennis Muilenburg, Boeing CEO commented: “This will allow us to prioritise additional resources to focus on software certification and returning the MAX to flight.”

April 29

In an address to shareholders, Muilenburg said the company was making “steady progress” on the path to certification. At this point, the firm had completed an official engineering test flight of the software — the final technical flight test prior to the certification flight.

A total of 400 airframes are awaiting certification and delivery once the grounding is lifted. Boeing

Test pilots had conducted 146 737 MAX flights, totalling around 246 hours of airtime with the updated software.

May 16

Just under a month later, Boeing conducted a further 61 flights with the new software, bringing the total flying time to around 360 hours.

The firm also announced it had completed the development of the updated software for the 737 MAX, along with associated simulator testing.

A statement released on that date, read: “Boeing is now providing additional information to address FAA requests that include detail on how pilots interact with the airplane controls and displays in different flight scenarios. Once the requests are addressed, Boeing will work with the [regulator] to schedule its certification test flight and submit final certification documentation.”

June 18

Three months after its best-selling jet had been grounded, Boeing made an appearance at the Paris Air Show.

While its European rival, Airbus, snapped up orders left, right and centre for its narrowbody variants – ending the show with 243 commitments – Boeing received a single letter of intent from International Airlines Group (IAG) for 200 737 MAX aircraft. It was the type’s only trade at the event, accounting for almost 70% of the company’s airliner orders.

June 26

The manufacturer experienced a setback in its mission to get the type back in the skies. In a statement, Boeing said it had uncovered a data processing issue, which impacted the pilots’ ability to perform the runaway stabiliser procedure which was required to respond to MCAS errors.

The problem was identified by the FAA during its review of the software update, which involved a number of simulator sessions.

The statement read: “Addressing this condition will reduce pilot workload by accounting for a potential source of uncommanded stabiliser motion.”

October 25

Responding to the final report by Indonesia’s National Transportation Safety Committee (KNKT), Boeing said it had redesigned the way the angle of attack (AoA) sensors worked with MCAS.

A statement from the Seattle-based firm read: “MCAS will now only turn on if both AoA sensors agree, will only activate once in response to erroneous AOA, and will always be subject to a maximum limit that can be overridden with the control column.”

“These software changes will prevent the flight control conditions that occurred in this accident from ever happening again.”

November 11

By this date, Boeing was continuing to work through additional requirements the FAA had identified. The airframer said in a statement that the timing of the type’s return to service was being dictated by the regulator.

The manufacturer was continuing to target the FAA certification of the MAX flight control software during the final quarter of 2019. The statement continued: “Based on this schedule, it is possible that the resumption of MAX deliveries to airline customers could begin in December…In parallel, we are working towards final validation of the updated training requirements, which must occur before the MAX returns to commercial service, and which we now expect to begin in January [2020].”

November 22

Boeing unveiled its first 737 MAX 10 flight-test aircraft at a low-key event in Seattle attended only by staff at the company.

MAX 10 Debut
The MAX 10 is not just a stretched variant, it also has special telescopic landing gear assemblies to count the increased length of the fuselage. Boeing 

The largest variant of the MAX family, the -10 can seat up to 230 passengers.

November 26

Boeing lost its approval to certify each of its jets prior to delivery after the FAA revoked its Organisation Designation Authorization (ODA) to issue airworthiness certificates prior to acceptance by customers.

In a letter to Boeing, the regulator wrote: “The FAA will retain such authority until the agency is confident that, at a minimum, Boeing has fully functional quality control and verification processes in place; delivery processes are similarly functional and stable; and Boeing’s 737 MAX compliance, design, and production processes meet all regulatory standards and conditions for delegation and ensure the safety of the public.”

December 17

In a sign that the recertification process was going to be delayed into 2020, Boeing announced that it would be suspending production of the type from January the following year.

The 737 MAX family of aircraft are assembled at Boeing's Renton facility in Washington. Boeing

In a statement, the airframer said: “This decision is driven by a number of factors, including the extension of certification into 2020, the uncertainty about the timing and conditions of return to service and global training approvals, and the importance of ensuring that we can prioritise the delivery of stored aircraft.”

December 23

As Christmas approached, it was all change at the top as Dennis Muilenburg, the company’s chief executive officer and Board director, resigned with immediate effect.

Board chairman, David Calhoun, assumed the role on January 13, 2020.

David Calhoun (pictured) took over the top job following the resignation of Dennis Muilenburg. Boeing

A statement said the Board of Directors believed a change of leadership was required to “restore confidence in the company moving forward as it works to repair relationships with regulators, customers, and all other stakeholders.”



January 7

In a change from previous recommendations, Boeing now advised 737 MAX simulator training in addition to computer-based instruction for all MAX pilots prior to return to service.

This moved away from one of the initial selling points for the type, which was that no simulator training would be required for pilots when they switched to the next-generation variant.

January 20

Boeing stopped production of the 737 MAX at its Renton facility in Washington. The airframer had announced its decision to halt manufacturing on December 17 2019.

January 21

The following day, a statement was issued by Boeing which said that its newest “best estimate” for when the type would return to service was now “during mid-2020”.

January 29

In its annual results for 2019, Boeing reported its first annual loss since 1997, a sign that the 737 MAX groundings were taking their toll on the American airframer.

The Chicago-based firm said it lost $636m last year, in stark contrast to profits in excess of $10bn in 2018.

April 29

The company’s first quarter results showed similarly gloomy figures. Boeing said it lost a further $641m in this period, mainly due to the effects of the COVID-19 pandemic and the 737 MAX groundings.

May 27

After a 128-day suspension, Boeing announced it had resumed production of the type at its Renton facility in Washington.

Throughout next year, production rate will be scaled based upon demand. Boeing

Beginning at a “low rate”, the construction will be ramped up production this year. The company plans to increase production to 31 airframes per month during 2021, with “further gradual increases to correspond with market demand”.

June 29

A three-day certification test campaign for the type is due to begin. According to Reuters, the FAA has completed a review of Boeing’s safety system assessment, clearing the way for certification flights to begin.

The type's first flight took place on January 29, 2016. Boeing

After nearly 500 days on the ground, the end could soon be in sight, with this week marking a pivotal point in Boeing’s journey to get the 737 MAX back in the skies. If all goes well, we could see the manufacturer reintroduce the aircraft to service near its last estimate of a “mid-2020”, although it’s likely to be solidly in the second half of this year.

The COVID-19 pandemic has naturally deflated demand for the jets, but as countries start to ease lockdown restrictions and people start travelling again, airlines – which were likely to be relieved that they didn’t have the burden of additional aircraft during the pandemic – will start to want to take delivery of their new examples.