These are key issues.
How significant is the Boeing 737?
This is the plane that, more than any other, helped to democratise aviation. The 737 is the world’s most successful airliner in terms of numbers sold. Over the past half-century, more than 10,000 have been built – placing it well ahead of its main competitor, the Airbus A320.
The twin-jet is the workhorse for many airlines – including Ryanair, which flies the 737-800 exclusively, and America’s biggest budget carrier, Southwest.
What is different about the Max version?
Boeing needed to offer airlines a more efficient twin-engined jet. The firm could have designed a new plane, but chose instead to continue the 737’s evolution. A commercial virtue of this approach is “commonality” – the idea that pilots trained on the current generation of the aircraft could transfer to the Max with minimal training.
The latest variant, which began flying in scheduled service two years ago, uses largely the same airframe, but its engines are much larger – a development that improves the fuel efficiency of the aircraft.
The Boeing 737 sits much lower on the ground than its more modern counterpart, the Airbus A320. This feature enables passengers to board and leave the plane using its own internal steps, and allows easier access for engineers.
But it also presented Boeing designers with a challenge. If the latest large engines had simply been hung from the wings, as on previous versions, there would have been insufficient ground clearance.
The problem was solved by mounting the engines higher, so they are blended into the wing and significantly further forward. This change has aeronautical consequences, however. In some circumstances the aircraft can tilt upwards, increasing the risk of a stall – in which the wings do not generate sufficient lift to keep the plane flying safely.
How was this problem addressed?
With new software called the manoeuvring characteristics augmentation system (MCAS). The anti-stall system monitors the angle between the wing and the airflow, known as the “angle of attack”. This is measured by a vane on the outside of the aircraft. If the system detects that the angle is getting dangerously steep, it operates an elevator in the tail to nudge the nose downwards – and does so repeatedly, even overriding the pilots’ commands.
On 29 October 2018, a Boeing 737 Max operating as Lion Air flight 610 took off from Jakarta. A single faulty angle-of-attack sensor triggered the MCAS response. It initiated a fatal struggle between the pilots and the anti-stall system. As the captain and first officer wrestled with the controls, MCAS repeatedly pushed the nose of the plane down, leading to a crash that killed all 189 passengers and crew.
What happened in the wake of that tragedy?
Boeing issued advice to 737 Max operators and pilots about how to combat an erroneous deployment of MCAS. But on 10 March 2019, Ethiopian Airlines flight 302 crashed at high speed shortly after take-off from Addis Ababa, with the deaths of 157 passengers and crew.
Initial investigation showed the pilots were fully aware of the problem and responded appropriately. But the cockpit voice recorder and black-box investigators revealed another battle between two men and the technology installed on one of the world’s most modern aircraft.
As more became known about the cause of the crash, aviation authorities around the world began to ground the Boeing 737 Max. But even as the UK’s highly respected Civil Aviation Authority (CAA) banned the plane from British airspace, the FAA insisted there was no fundamental problem with the aircraft.
Around 24 hours later, the FAA also issued a grounding order.
What do the safety authorities want to know?
They want answers to a series of specific questions about what improvements have been made to the anti-stall software by Boeing engineers; changes in procedures; and what training the planemaker proposes to offer in order to ensure that flight crew worldwide are familiar with the new system and its limitations.
But they will also ask searching questions about the initial certification of the Boeing 737 Max. There have been repeated accusations that the manufacturer and the FAA have grown too close, with the safety regulator failing adequately to challenge the designers.
In the process, the principle of redundancy, which allows for multiple failures without jeopardising the aircraft, appears to have been overlooked. For a plane to crash as a result of events triggered by a single failure – in these cases, the angle-of-attack sensor – goes against the whole philosophy of aviation safety.
During previous groundings, most notably of the Boeing 787 Dreamliner in 2013, the world was content to take the lead from the FAA. That may not happen again.
What is the effect of the grounding?
This is the busiest summer for aviation worldwide, and the inability to fly more than 500 aircraft has caused big problems for a number of airlines including American Airlines, Norwegian, Tui and Ryanair – which was due to start flying a specially designed Boeing 737 Max, the -200 version, in May.
Extra capacity is being chartered in to maintain schedules, but some flights are being cancelled. The cost to the airlines is running into billions of pounds. In May, Tui said the costs incurred for chartering in aircraft and other measures to deal with the grounding will range from €200m – if the plane is allowed to fly in time for the peak month of August – to €300m if the grounding continues until the end of the summer.
A meeting in Fort Worth, Texas, in May heard that the FAA has no timetable for returning the Boeing 737 Max to service. The acting administrator, Dan Elwell, has said: “If it takes a year to find everything we need to give us confidence to lift the order, then so be it.”
What has this done to confidence in Boeing?
The whole sad saga has proved extremely damaging for the manufacturer’s reputation among airlines, pilots and passengers. The Boeing 787 Dreamliner grounding, which lasted four months, was imposed after a series of battery fires, none of which harmed the travelling public. There is now widespread acclaim for that aircraft.
But defects in the 737 Max are implicated in two calamitous tragedies. Even when the grounding order is lifted, concern is likely to remain.