Boeing 737 Max: What needs to happen for it to fly again?

Boeing boss Dennis Muilenburg warned he may have to stop production of the troubled jet involved in two tragedies if does not fly again soon

After Boeing announced a $3.4bn (£2.7bn) second-quarter loss as a result of the 737 Max grounding, the manufacturer’s boss has outlined plans for the plane’s return to the skies. But what needs to happen before the aircraft re-enters service?

Here is everything you need to know.

The tragic events that led to the worldwide grounding

The Boeing 737 is the most successful airliner in history. But the latest variant of the twin-jet plane was grounded worldwide after two fatal crashes killed a total of 346 people.

In both the Lion Air accident in October 2018 and the Ethiopian Airlines crash in March 2019, an anti-stall system known as the Maneuvering Characteristics Augmentation System (MCAS) was blamed.

The system was installed as a fix for the problem created by installing bigger engines, and moving them higher and further forward on the wing.

In each tragedy, an “angle of attack” sensor – which measures the angle between the aircraft wing and the airflow – gave a false reading, indicating a possible stall condition. In response, the MCAS software tilted the aircraft nose down relentlessly as the pilots battled to save the plane.

In the wake of the second tragedy, Boeing and its US regulator, the Federal Aviation Administration (FAA) initially insisted that the Boeing 737 Max was safe. But as more evidence emerged from Ethiopian investigators, the plane was grounded worldwide.

The manufacturer said: “Boeing continues to have full confidence in the safety of the 737 Max,” but added that it was recommending the entire global fleet of 371 of the type be grounded “out of an abundance of caution and in order to reassure the flying public of the aircraft’s safety”.

Hundreds more Boeing 737 Max aircraft were due to be delivered but are still on the ground.

What was the effect on Boeing – and the wider aviation industry?

Between April and June 2019 its commercial plane deliveries fell by more than half to 90. Payouts to airlines whose planes are standing idle, as well as carriers expecting deliveries of the aircraft, are estimated to cost the planemaker $4.9bn (£3.9bn).

Airlines including Norwegian, Tui Airways and Ryanair have cut back services while they wait for the plane to return to service.

While Ryanair – Europe’s biggest budget airline – has no Boeing 737 Max jets in its fleet at present, it has 210 of a special high-capacity variant of the aircraft on order.

Deliveries were due to begin in April 2019, with flights starting in May.

Many other carriers, including American Airlines, Southwest and Turkish Airlines, have large gaps in their fleets caused by the grounding.

What is the process for returning the Boeing 737 Max to service?

The FAA, other aviation regulators and the airlines must be convinced that the MCAS issue is resolved and that the aircraft is wholly safe.

The European regulator, EASA, as well as Transport Canada and other regulators from around the world are checking the homework of Boeing and the FAA on the millions of lines of software code that are needed for the MCAS system.

Dennis Muilenburg, Boeing’s chairman, president and chief executive, says: “We do have to go through a multi-regulator approval process and it's a complex process and one that will take time to get done.”

Pilots working for both the regulators and the airline customers are testing the changes in flight simulators.

In addition, a separate software problem has been identified and requires further work.

“Last month, the FAA directed us to address a specific condition of flight unrelated to MCAS,” says Mr Muilenburg. “We agreed with the FAA's decision and we are currently working on the software changes to address this requirement.”

The company says: “Addressing this condition will reduce pilot workload by accounting for a potential source of uncommanded stabiliser motion."

What is the timeline?

The regulators stress there is no schedule for returning the jet to commercial flying. The maker says: “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.”

But Boeing has now outlined its own timetable.

The planemaker believes it will receive certification and operate proving flights in September.

“Our best current estimate is a return to service of the MAX that begins early in the fourth quarter,” says Mr Muilenburg. Boeing’s fourth quarter runs from October to December, so presumably he means October.

Will the plane start flying worldwide once a green light is given?

Not necessarily, and not immediately. Pilots and their trade unions will need to be convinced the modifications eliminate risk. Captains and first officers will require additional training on the changes made by Boeing. If additional simulator training is required, that will slow things down.

There is also the possibility that, for example, the FAA might give permission for a return to service, while other global aviation regulators do not.

US carriers could reinstate services domestically. But that would immediately cause conflicts: if the UK Civil Aviation Authority failed to give the go-ahead, then passengers booking “codeshare” flights with British Airways could find themselves on Boeing 737 Max flights operated by American Airlines; the same could apply to Virgin Atlantic/Delta.

What if the delay continues?

“We might need to consider possible further rate reductions or other options, including a temporary shutdown of the Max production,” says Mr Muilenburg.

“Every day we are doing scenario planning, working through every dimension of this program. We're looking at the ongoing software update development, the regulatory approvals, the certification process, the return to service process, working hand-in-hand with our customers.

“We understand the ripple effects of any changes to the schedule and we're going to continue to monitor that on a day-to-day basis.”