The United States Federal Aviation Administration lifted the grounding order on Boeing's 737 MAX airliner on Wednesday 18 November 2020.
Following 20 months of rivet by rivet scrutiny of the airliner by the FAA and several other worldwide aviation safety bodies such as the European Union Aviation Safety Agency plus several thousand hours of testing by groups of international safety advisers and airline pilots, it has been cleared to return to the skies.
An airworthiness directive has been issued mandating changes to the aircraft and the training of aircrew on the type.
Other regulators, such as the those in Canada and the far East have yet to follow the FAA lead but are expected to rescind their grounding orders in due course once the changes made to the aircraft and the training procedures of the airlines operating it, have been carried out.
Given that it has been so long since the airliner was grounded, perhaps it is apposite to briefly summarise the saga.
The Boeing 737 MAX is a development of the 50 year old Boeing 737 design. This airliner type has been one of the most popular and best-selling narrow-body jet airliners ever built. It has, in its 737-800 iteration, proven to be an almost flawlessly safe and reliable aircraft.
The MAX derivative was modified by the installation of more powerful, more efficient high bypass turbofan engines. These engines make it one of the most efficient airliners available in its class.
The new engines brought about a slight change in the handling of the aircraft at extremes of the flight envelope (not normally enountered, it was thought) and Boeing installed a system to keep the handling characteristics the same as the older generations of the 737 design.
The system, if it detected that the airliner was about to stall (lose lift), would force the nose down by changing the angle of the rear horizontal control surface. The system, however, relied only on one sensor (known as the angle of attack sensor) to feed information to the control computer.
In addition Boeing had assumed that the training and professional standards of the aircrew that would be flying the airliners would be of such a nature that any malfunction of the system would be correctly identified and mitigated using cut out switches in the cockpit.
Sadly, however, the average level of experience and training of aircrew in non-first world countries had declined to such a point that, in some cases, some crew members placed in the cockpits of airliners have less than 350 hours of total flight experience.
In the event, two airliners on which this single sensor had developed faults or were not serviced properly, crashed within months of each other after the faulty sensors repeatedly activated the augmentation system.
In both accidents it has subsequently been found that the aircrew involved did not cross check their situation properly, did not communicate as effectively as they might have and failed to make correct use of a decades old standard operating procedure which could have let them to de-activate the system.
The aircrew on both flights, however, were confused as to the actions of the aircraft due to something known in aviation safety as “the startle factor” and “automation surprise” which led them to mismanage what were, in reality, recoverable situations.
Nevertheless, the 737 Max type was grounded as the assumptions made and the reliance on just one component plus the fact that training standards of aircrew were not as high as had been assumed, were obviously aspects that needed urgent attention.
In the period of the grounding, a re-design of the augmentation system, its inputs, operational logic, crew training on the system and all other parameters was undertaken.
The nett result is that the changes made to the manoeuvring augmentation system will not allow the system to repeatedly malfunction again and have placed limits in its authority, even with faulty components or mishandling of the airliner by the crew.
Before it can fly again, however, the new components feeding information into the augmentation system (Multiple sensors with cross checking and redundancy), updated software and warning systems need to be installed in all aircraft already with operators and those constructed but not yet delivered.
In addition, crews operating the airliner must undergo new simulator training related to the changes and the airliner itself and may no longer simply transfer to the type from older 737 models without this type-specific training.
Finally, all aircraft that have been parked by airlines since the grounding have to undergo a specific set of inspections and service mandated by the FAA before being allowed to fly revenue flights again.
The several thousand hours of flight tests by the FAA, airline crews, worldwide safety agencies and others have now proven that the sum of changes made to the 737 Max have, in the view of many industry experts, resulted in an airliner which will now, arguably, be the safest airliner to ever take to the skies.
Airlines around the world are now very busy preparing their examples of the type to return to revenue service in time for the upcoming year end travel period.
Boeing suppliers, staff and shareholders are, no doubt, breathing a sigh of relief.
The entire episode, however, has highlighted several inter-related aspects of the aviation safety chain that have, perhaps, become a little too cozy and familiar in the past decades of near faultless operation of the supply, training and operation of commercial jet aircraft.
The ripples throughout the system will, hopefully, have a wider and far more permanent positive impact on the industry and safety than just the changes to this one one aircraft type.
It has, perhaps, provided a timely wake-up call to every role player in commercial aviation to re-evaluate what is normal and not to rely on automation to the exclusion of good basic manual flying skills, correct, clear communication and old-fashioned experience on the flight deck.
Mark D Young is a South African investigative journalist and aviation safety author.