By: Gareth
Published on: 19 January 2024, 9.00pm (GMT +8)
A China Southern Boeing 737 MAX 8. Photo: Haotian (instagram.com/plane.tian)
When American Airlines announced its decision to order 260 Airbus A320 jets in July 2011, few would have thought that the defection of a single loyal Boeing customer would lead the commercial aviation world down a rabbit hole that eventually led to an Alaska Airlines plane suffering a widely-publicised blowout last week. Yet here safety experts worldwide are, forced for the second time in a decade to scrutinise Boeing and its controversial decision to hastily put together a re-engined 737.
The history of the Boeing 737 MAX series is by no means as simple as skimming over the accidents that made it infamous. The question of why Boeing developed it and what caused so many reliability problems requires us to embark on a journey down a rabbit hole of our own to find out more…
Bravo, Anakin. You’ve done it again.
As usual, it began with a press conference. Airbus SE launched the A320 NEO programme in 2010, declaring that the new CFM LEAP and Pratt & Whitney 1000G engines would reduce fuel burn and increase operating efficiency. In response to this, Boeing CEO Jim McNerney ordered intensive research into a possible competitor for the A320 NEO. Boeing had already been looking into a replacement for the 737 since 2006, but now the goal was not to replace the 737NG series, but to re-engineer it and in doing so build the most fuel-efficient commercial narrow-body the world had ever seen.
By the turn of the 2010s, Boeing was by no means a stranger to threats by Airbus. Time and time again, with the A330, then the A350 and A380, Boeing had risen to the challenge and produced successful competitor aircraft: clean-sheet designs for the 777 and 787 and a remastered 747. Without the benefit of foresight, the engineers’ task to build a more fuel-efficient narrow-body seemed very much achievable. And for a while, industry watchers thought they had succeeded once more.
A new narrow-body for the future…
The first Boeing 737 MAX 8 rolling out of Renton. Photo: Getty Images (gettyimages.com)
The first 737 Max 8 rolled off the assembly line in Renton in August 2015 with several aerodynamic enhancements. Firstly, a split-tip winglet reduced fuel consumption by up to 1.8% at full load. The tail cone had also been recontoured, revising the APU inlet and exhaust.
The most important enhancements to the 737 were the new engines. The new CFM LEAP-1B engines were promised to be up to 12% more efficient than the CFM56-7Bs of the 737NG, and nearly 40% quieter. Other enhancements including a phenomenal increase in overall pressure ratio resulted in an additional 385 kg of weight added to the engines.
The heavier engines were one of the factors that resulted in modifications to the rest of the airframe. Maintaining the project’s aim to be more efficient than the A320NEO, Boeing Commercial Airplanes CEO Jim Albaugh opted for a 68-inch turbofan with a higher bypass ratio which necessitated an extension of the landing gear by 15 to 20 cm to maintain a 43cm ground clearance. A side effect of this was that the larger nacelles were placed more forward on the wing, increasing the pitch rate of the aircraft when airborne. Note the emphasis on the bold phrase. This was Accident Factor Number 1 - that the aerodynamics of the aircraft favoured an automatic pitch up.
Accident Factor Number 2 requires us to examine the software of the aircraft. The systems on the Boeing 737 Max were designed to be as similar to that of the 737NG as possible to allow 737NG pilots to fly the new type with minimal recertification. One of the measures introduced to allow this was to introduce a system known as the Manoeuvring Characteristics Augmentation System (MCAS), which was to automatically initiate a pitch down to cancel out the pitch-up tendency caused by the engine position. On paper, this looked perfect as MCAS was an automatic system that could not be overridden by pilot input. More seriously, a description of MCAS was not included in the operating manual, leaving pilots with no idea that there was an inbuilt pitch-up tendency, nor that the ability of the aircraft to fly in a straight line was at the mercy of a single, hastily-developed software that had undergone limited testing, having only been programmed after the first test flights. The bold phrases here summarise Accident Factor Number 2.
…or not
So now we have our answer to the Max’s lack of reliability - poor aerodynamic design and an unreliable software. MCAS was programmed to adjust the elevators to pitch down automatically to correct whatever additional pitch-up tendency there was, as measured by the Angle of Attack (AoA) sensors. The problem now is that if an AoA sensor malfunctions and the MCAS overcorrects the pitch up, it could send the aircraft into a nosedive with no way for the pilots to manually override it. And it is this flaw in the software design that proved fatal.
Sometime after dawn on 29 October 2018, Lion Air Flight 610 plummeted into the Java Sea off the coast of Jakarta, killing all 189 people on board. Workers from a nearby oil platform informed authorities that the aircraft had crashed with an unexplainably steep nose-down angle, which prompted an investigation into the MCAS software. The flaw of the MCAS in relying solely on AoA sensor data was finally discovered and advisories sent to all 737 Max operators worldwide, but these were not followed though in time.
The aircraft, PK-LQP, involved in the accident. Photo: Wikipedia (wikipedia.org)
Less than five months later, Ethiopian Airlines Flight 302 crashed into a farm field after experiencing software glitches eerily similar to that of the Lion Air flight. The second time, though, the pilots had managed to disable the MCAS by disabling the electrical trim tab system, but this also prevented them from trimming the aircraft using the switches on the wheel. In desperation, Captain Yared Getachew tried to crank the trim wheel by hand but was unsuccessful and could only watch helplessly as the aircraft met the ground at 1100 km/h, killing all passengers and crew on board.
ET-AVJ, the airframe involved in Flight 302. Photo: Wikipedia (wikipedia.org)
Back to the present
We all know what happened next. The groundings, the re-certification and re-entry into service in 2020. We thought the 737 Max’s problems were over, but then 2024 began and the world appeared to be unsatisfied with one widely-publicised accident at Tokyo Haneda Airport.
Last week, an Alaska Airlines 737 MAX 9 flying to Ontario, California from Portland, Oregon, suffered a blowout mid-flight when a door plug detached from the airframe mid-flight, causing a rapid depressurisation. No injuries were reported from the incident.
The side panel blown out of the 737 MAX 9. Photo: @strawberrvy (instagram.com/strawbervy)
On one hand, the world breathed a sigh of relief at finally having a 737 accident that didn’t have to do with the faulty MCAS. But what lies ahead for the type? Only time will tell.
boeing should stop production for MAX