The Boeing 737-8 MAX issue explained

Mark Young examines what could be behind the two recent crashes of the newly introduced airplane

We Africans have had the name of the Boeing 737-8, also called the 737 MAX, vividly engraved on our collective psyche in the past few days.

For us in the southern reaches of the continent, doubly so.

On Sunday morning, OR Tambo International Airport saw an Ethiopian Airlines Boeing 737-8 MAX registration ET-AVJ depart for a routine journey to Addis Ababa, Bole Airport.

The aircraft involved was one of four of this new derivative of the long-serving Boeing 737 the airline had in service. It had been delivered in October 2018, making it barely five months old.

A few hours later, after an ostensibly incident free trip from South Africa, while taking off on its next flight number 302 out of home base, the airliner impacted high ground near the town of Bishoftu after barely 6 minutes of flight time.

The Boeing 737-8 MAX has nearly 370 siblings worldwide. It has been in service since 2017 and has completed more than a quarter of a million scheduled flights with superb reliability and efficiency.

As the latest development of Boeing's ubiquitous single aisle jetliner that first entered service in the late 1960s, it has amassed more than 5000 orders, making it the fastest selling jetliner in the history of the Seattle manufacturer.

So, why have nearly half the operational fleet around the world, including the sole example delivered of a sizeable order for local operator Comair, been grounded by their operators and aviation authorities in several countries?

Civil aviation safety is predicated on a multi-layered approach to safety. 

From initial design to testing, manufacture, certification and constant revisions to procedures, crew training and other processes honed from operational safety audits and the study of the smallest incidents, the industry has – in well managed jurisdictions – a robust approach to safety that leaves nothing to chance.

This process has become so keenly applied that in the past 3 decades several different types of airliner have been introduced to service with no losses for many years following their first flights.

In 2015 there were no passenger fatalities on scheduled jet airline transport flights anywhere in the world! This statistic alone stands as a huge motivator in the unfolding story of the Boeing 737-8 MAX and the modern approach to air transport safety.

In October 2017, Lion Air flight 610 operated by a Boeing 737-8 MAX was lost into the sea 12 minutes after take-off. There were no survivors. That aircraft too was new, having been delivered just two months prior to its loss.

During the subsequent investigation the local authorities were – initially – only able to find the digital flight data recorder, one the two orange recorders that assist in re-creating the circumstances of an airliner accident.

From the data they recovered they found that the aircraft had stalled and dived into the sea after the crew failed to keep the altitude of the aircraft under control. The exact circumstances of how and why this happened are still being determined. The cockpit voice recorder was only found in January this year and the human factors at play that led the crew to lose situational awareness with such tragic consequences will, in time, come to light.

However, perusal of the maintenance records of the aircraft revealed that previous flights had led to faulty indications on some instruments and the crews involved had switched off the electric trim system after repeated activation of the trim system had made maintaining level flight difficult.

This repeated trimming of the aircraft had been initiated due to faulty sensor inputs to a system known as the Manoeuvring Characteristics Augmentation System (MCAS).

This system is designed to prevent the airliner flying into a stall at high angles of attack.

It achieves its intended aim by driving a motorised adjustment system that trims the airliner's nose downwards. If this system is triggered accidentally due to faulty information from sensors – as seems to be the case in the Lion Air accident flight - the aircraft will reduce altitude.

There are conflicting reports worldwide regarding the amount of data provided to airlines on this system by the manufacturer. Some airlines and pilot's unions expressed surprise to learn about this system while many others knew of its existence and had trained crews in its use and deactivation.

The operation of the system is easily felt through forward pressure on the control column, however, and the MCAS system can easily be over-ruled by use of a trim switch on the pilot's control column or by virtue of good old fashioned muscle power by grabbing the trim wheel and holding it in place.

As a final resort, the system can be switched off entirely. The Boeing 737 has had a Runaway Trim memory item in the pilot's handbook since inception. The ultimate solution has been the same for 50 years plus - Switch it off and fly the aircraft while trimming manually.

With the MCAS system, if the electric trim switch is used to command the aircraft to trim upwards, the system disengages. However, if the input of data to the system is still making it think the aircraft is climbing too steeply, the MCAS system will re-activate after a period and drive the nose down again. By all accounts to hand to date, it appears that the faulty sensor which indicates the aircraft's angle of attack to the oncoming airflow on the Lion Air airliner had not been detected and repaired by the airline's maintenance crews.

This set of circumstances involving the sensor appears to have persisted for some days and previous crews had worked around the problem to safely conduct their flights. This they achieved by the simple expedient manually trimming the airliner – a process most rookie pilots of even light aircraft are taught to do almost from the outset. Some within the industry pointed to the fact that the previous flights had landed safely as proof that the system and the aircraft itself was not to blame in the first instance and that an alert crew applying good crew resource management (CRM) should not have had an issue.

And so the use of the 737-8 MAX continued. 

Until the 10th March 2019.

Sunday's loss of a MAX aircraft, so soon after the loss of the Lion Air aircraft, in circumstances that, to laymen, appear similar (soon after take-off, a new aircraft, a new model) has been amplified on social media – as with most events nowadays.

In addition, given the exceptional safety standards that have been achieved by airlines in recent years, the fact that two newly delivered airliners, of a new type, have crashed in a short space of time in ostensibly similar phases of flight, has sent waves through a very risk averse industry.

Even though nobody yet knows if the causes of the two losses are related and nobody yet knows if any of the systems on the airliner played a role in Sunday's loss, airlines have voluntarily grounded their aircraft. In some countries like China, the national regulator has mandated a grounding of the type.

South Africa's Comair said in a statement issued on Monday that the airline had “...decided to remove its 737 MAX 8 from its flight schedule, although neither regulatory authorities nor the manufacturer has required it to do so,...”

The operator re-iterated its “...confidence in the inherent safety of the aircraft...” but continued to say that “...it has decided temporarily not to schedule the aircraft while it consults with other operators, Boeing and technical experts.” 

The safety of crew and customers is, the airline stated, non-negotiable.

This en-masse voluntary grounding of an airliner type is a first in the annals of aviation safety as previously airlines have continued using types involved in accident clusters until regulators had mandated the grounding of the aircraft after the results of investigations had been collated.

However, in the modern age where news is instantly available and clients can easily share information, an over abundance of caution can be seen as not only good safety practice, but good PR.

It is highly unlikely, given the hundreds of thousands of incident free flights completed by the 737-8 MAX, and the hundreds of flights it is still completing with the balance of the worldwide fleet even as you read this, that the airliner itself is, in the first instance, at fault.

In time it is most likely that the airliner model will resume service and continue to amass a proud safety record.

In the interim, however, as both the orange data recorders of Ethiopian Airlines flight 302 have been found, initial answers will be rapidly forthcoming.

If services are resumed with the 737-8 MAX, then the decision to do so will be based on sound science and the facts gleaned from flight 302.

All airlines know that flight safety costs them huge amounts.

The cost of an accident, however, is incalculable.

And that is why half the world's B737-8's are on the ground at the moment.

It's cheaper than flying the odds and losing.


Wednesday 14 March 2019: Following a United States Presidential Executive order to ground Boeing 737-8 and 737-9 MAX airliners in the USA, the manufacturer of the Boeing 737-8 and 737-9 MAX airliners, Boeing, issued a statement yesterday to the effect that it supported the actions already taken worldwide.

The Boeing statement said “Boeing continues to have full confidence in the safety of the 737 MAX.  However, after consultation with the U.S. Federal Aviation Administration (FAA), the U.S. National Transportation Safety Board (NTSB), and aviation authorities and its customers around the world, Boeing has determined -- out of an abundance of caution and in order to reassure the flying public of the aircraft’s safety -- to recommend to the FAA the temporary suspension of operations of the entire global fleet of 371 737 MAX aircraft. 

“On behalf of the entire Boeing team, we extend our deepest sympathies to the families and loved ones of those who have lost their lives in these two tragic accidents,” said Dennis Muilenburg, president, CEO, Chairman of The Boeing Company.

“We are supporting this proactive step out of an abundance of caution. Safety is a core value at Boeing for as long as we have been building airplanes; and it always will be. There is no greater priority for our company and our industry. We are doing everything we can to understand the cause of the accidents in partnership with the investigators, deploy safety enhancements and help ensure this does not happen again.”

In the interim, the data recorders from the Ethiopian airliner are being sent to the United Kingdom for read-out.

Airline accident investigations are know to take several years to finalise although, usually, interim reports are issued within 30 days by ICAO member countries. Time will tell how rapidly answers are forthcoming and exactly how long the worldwide grounding will last.