About the two Boeing 737 MAX 8 accidents, the role of MCAS, communication and consequences, you can read here:
1. Larger Engines on the Boeing 737 MAX 8
The manufacturer intended to render its new Boeing 737 MAX 8 model more fuel-efficient. Hence, larger engines, the LEAP-1B model, were introduced. In order to fit these larger engines under the wings, leaving still enough space between them and the ground, they had to be mounted further forward and closer to the lower surface of the wings than the CFM56-7 engines on the previous model, the Boeing 737NG (Next Generation).
The size of these new engines and their placement cause a vortex off the nacelle, which, at a high angle of attack, AOA, produces lift. As the engines are in front of the centre of gravity, CG, this lift causes the planes to exhibit a slight tendency to pitch up (raise their noses).
This pitch-up tendency also means that the pilots need less force to pull the control column towards themselves if they want to climb. This was considered dangerous, as a crititcal AOA close to a stall is reached more easily. Therefore, when the sensors indicate that a critical AOA is approached, the resistance in the control column is intentionally increased.
Taken together, a solution was needed to counteract the AOA increase towards values at which a stall becomes more likely. As other measures, such as a revision of the leading edge stall strip, were not likely to pass certification, the manoeuvering characteristics augmentation system, MCAS, which already existed on previous models, was considerably modified. New automated features were introduced.
2. The Manoeuvering Characteristics Augmentation System, MCAS
On the Boeing 737 MAX 8, the MCAS could lower the nose of the plane automatically in reaction to the values provided by the angle of attack sensors. Each plane has two sensors, which are mounted on both sides of the nose and also called alpha vanes, but to activate the MCAS, only the value of one of them was necessary.
At the rear of the plane is the trimmable horizontal stabiliser, THS, which can be moved up and down. In accordance with this movement, the angle of attack, AOA, is increased (nose up), or decreased (nose down). Usually, pilots of Boeing airliners can use the switches on their yokes to trim the stabiliser, or the trim wheels in the centre console when manual trim is necessary.
As we said before, MCAS could decrease the AOA automatically. For this, the flaps on the wings had to be fully retracted.
When pilots had actively counteracted MCAS, this system was able to reset itself and repeat its action.
Example of a trimmable horizontal stabiliser. The empennage of a Boeing 737 MAX 8 is built in the same fashion. Photograph Schottdorf EM
3. MCAS During the Certification of the Boeing 737 MAX 8
As the certification process of an airliner is complex and as MCAS is of major interest in this case, we will concentrate on that system here.
3.1. Competition and Financial Interests
Boeing´s competitor, Airbus, had launched the more fuel-efficient A330neo, which was a major success. As American Airlines contemplated to purchase this airliner, Boeing needed to respond quickly. Constructing a new type of airliner would have taken years of development and a large investment.
Furthermore, a new type of aircraft involves extensive simulator training, which is very expensive for the airlines. Purchasing an Airbus A330neo, or a completely new Boeing would have involved such costly training, whereas buying a new plane of the type, which an air carrier already has in its fleet, does not.
Hence, Boeing wanted the new aircraft to be regarded a variant of the existing 737s. In order to obtain a certification for the Boeing 737 MAX 8 as such a variant, the company had to downplay the innovations and the augmented features of the MCAS.
3.2. The Communication About MCAS on the Boeing 737 MAX 8
When Boeing handed in the paperwork, it managed to convince the Federal Aviation Administration, FAA, that the changes to the MCAS were so negligible that they would not need to be particularly emphasised.
The training, which is necessary to fly a novel model of the same type, may be delivered as a computer programme and can be completed on a tablet. This programme informs the pilots about all changes that have been made in comparison to the previous model. In case of the Boeing 737 MAX 8, the MCAS was not included.
Therefore, pilots did not learn about the scope of the new and automatic features of MCAS when the Boeing 737 MAX 8 was certified in March 2017. These features were not disclosed in the pilot´s handbook, either, leaving the pilots without any chance to know about the system, and, even worse, to counteract its unwanted activation sufficiently.
3.3. The Organisation Designation Authorisation Programme (ODA) of the FAA
The so-called Organisation Designation Authorisation Programme of the FAA leaves certain parts of the certification process to the manufacturer itself. This, in turn, diminishes the oversight which the FAA has over how Boing handles the details and what exactly the technical innovations entail. During the certification of the Boeing 737 MAX 8, this resulted in a considerable misunderstanding of the MCAS (1).
1) U.S. Department of Transportation, Office of Inspector General (2021) Weaknesses in FAA´s Certification and Delegation Processes Hindered Its Oversight of the 737 MAX 8. Report No. 2021020
4. The Accident of Lion Air Flight 610 on 29 October 2018
On October 29th, 2018, the two pilots (captain Bhavye Sunaja, 31, and first officer Harvino, single name) commenced their flight, LT 610, in daylight and "good" weather conditions. The Boeing 737 MAX 8, which was used on that flight, was registered PK-LQP.
The route was planned to lead from Soekarno International Airport, Jakarta, Indonesia, to Pangkal Pinang, Indonesia. In the cabin, there were 181 passengers and six flight attendants.
4.1. What happened in the Cockpit of the Boeing 737 MAX 8 Before the Crash?
Preflight Briefing and Taxiing out to the Runway
- during the preflight briefing, the technical issues, which had been logged after the flight before (addressed below), were not mentioned
- as the pilots taxied out to the runway, the left primary flight display, PFD, indicated a pitch attitude of -1° and the right one +13°
Take-off and the Beginning of the Climb
- the pilots took off from runway 25L at 06:18 local time
- two seconds after lift-off, the left stick shaker was activated (audible and fast vibration of the control column to alert pilots to an imminent stall)
- the take-off configuration warning system sounded its alarm
Unreliable Indications of Speed and Altitude
- at 06:20, the pilot monitoring, PM, in that case the first officer, stated: "indicated airspeed disagree" (a difference of 5 knots for more than 5 seconds between the left and right PFD, abbreviated IAS)
- the first officer asked whether they should return to the airport, but he did not get a response (from a CRM point of view: problematic communication and assertiveness, but we must be caucious, the hierarchy might be different)
- as the left PFD indicated an altitude of 790 feet, and the right one 1040 feet, the crew asked ATC to verify their altitude: on the radar display it was 900 feet
- at 06:21 and 45 seconds, the crew alerted ATC that they had a "flight control problem", they did not declare PAN PAN PAN (alerts ATC to prioritise this message, as the crew might need assistance in a potentially hazardous situation)
- at 06:22, the crew started to retract the flaps, and once they were fully retracted an automatic aircraft nose down, AND, was activated for 10 seconds
- when the crew extended the flaps again, this action stopped, but it returned after repeated flap retraction
The Continued Automatic AND Commands of the Boeing 737 MAX 8
- in total, more than 20 automatic AND commands happend, and each of them was counteracted by the pilots
- their aeroplane could not climb steadily, rather, the changes in altitude were considerable, with a rate of descend of up to 3200 feet/minute
- at 06:31 and 43 seconds, the hidden MCAS caused the airliner to pitch downwards into an almost vertical nosedive
- the ground proximity warning system, GPWS, detected the surface of the sea, and the warning "terrain, terrain", followed by "pull up, pull up" sounded
- at 06:32, the communication with ATC stopped
What must the pilots have felt as they tried to counteract the ongoing uncommanded nosedives of their Boeing 737 MAX 8, which involved an increasing resistance in the control column?
4.2. The PK-LQP Flight Which Preceded Lion Air Flight 610
The aircraft registered PK-LQP was used on a flight from Denpasar to Jakarta on 28 October 2018. In the preflight briefing, the captain mentioned that one AOA sensor had been replaced and tested accordingly (2).
The events on this flight unfolded as follows:
- after an uneventful take-off, at an altitude of about 400 feet, an IAS disagree warning was shown on the primary flight display
- the stick shaker was activated (audible and fast vibration of the control column to alert pilots to an imminent stall)
- the captain, who was pilot flying, PF, handed the control over to his first officer, as he intended to explore the cause of the problem
- the left PFD seemed to be malfunctioning
- acceleration and flap retraction were continued as usual
- the captain noticed that, whenever his first officer stopped his trim input, an automatic AND command occurred
- after three of these unwanted dips of the plane´s nose, the first officer stated that the control column was hard to pull aft
- PAN PAN PAN was declared to ATC
- the switches in the middle console were set to STAB TRIM CUT-OUT, and the AND commands stopped, switching them on again immediately brought back the problem
- the switches were, therefore, set to CUT-OUT again
- three non normal checklists, NNCs, were performed, unreliable airspeed, unreliable altitude, and runaway stabiliser (performed when the pitch trim wheels start rotating without stopping, which indicates that the stabiliser is being trimmed continuously)
- the pilots managed to land the plane safely at Jakarta airport
The crew applied important checklists. The pilots also managed to stop the input transmission from MCAS to the stabiliser by setting the STAB TRIM switches to "CUT-OUT", which stopped the nosedives. However, it is important to note that MCAS and its hidden actions were not mentioned at all in this course of events. After this flight, the captain informed a flight engineer about the problems and also logged them in the Aircraft Flight Maintenance LOG (AFML).
2) Komite Nasional Keselamatan Transportasi, Republic of Indonesia (2018) Preliminary Aircraft Accident Investigation Report, KNKT.18.10.35.04, PT. Lion Mentari Airlines, Boeing 737-8 (MAX); PK-LQP, Tanjung Karawang, West Java, Republic of Indonesia, 29 October 2018 (page 28 and following)
4.3. The Pilots´ Reactions to the Disaster
How must Boeing 737 MAX 8 pilots have felt when they learned that their colleagues had to deal with a hidden automated system which was malfunctioning?
Captain Daniel Carey, Union President of the Allied Pilots Association, stated in his remarks, which he had prepared for the hearing before the House aviation subcommittee:
"The huge error of omission is that Boeing failed to disclose the existence of MCAS to the pilot community. The final fatal mistake was, therefore, the absence of robust pilot training in the event that the MCAS failed."
4.4. Boeing´s Actions After the First Boeing 737 MAX 8 Crash
Boeing did at first not show any responsibility. In addition, the company did - at least publicly - not reflect on the role MCAS played in the crash of flight LT 610. Rather, it focused on the flight prior. to the fatal one and highlighted maintenance issues. Furthermore, it tried to blame the pilots for the mistakes they made, whilst at the same time expressing their condolences to the victims´ families and emphasising the importance of safety.
Pilot training was not changed to simulator sessions, but still delivered on a tablet after the first Boeing 737 MAX 8 accident.
5. The Crash of Ethopian Airlines Flight 302 on 10 March 2019
5.1. Technical Malfunctions on the Boeing 737 MAX 8 Registered ET-AVJ
In early December 2018, relevant maintenance works had to be carried out on the Boeing 737 MAX 8, which was later used on the accident flight. The reasons were temporary fluctuations of vertical speed and altitude indications, as well as a rolling of the plane to the left and right, which had occurred when the autopilot was engaged.
The unreliable indications of speed and altitude reoccurred prior to flight ET 302 and were addressed accordingly by maintenance personnel. However, as these fluctuations were intermittent, it was difficult to determine whether a permanent solution to this problem had been found (4, page 248).
5.2. The Planned Flight From Addis Ababa, Ethiopia, to Nairobi, Kenya
Flight ET 302 was scheduled to take off from Bole International Airport and carry its passengers to Jomo Kenyatta International Airport. The captain, 29, was going to be the pilot flying, PF, and his first officer, 25, was going to be pilot monitoring, PM. On board, there were also six cabin crew and 149 passengers.
5.3. The Events on Flight ET 302 Before the Crash
Take-off Roll, Lift-off, and the Beginning of the Climb
- at 05:37 and 51 seconds, the pilots began their take-off roll, which was followed by a normal lift-off
- immediately after take-off, erroneous AOA values were displayed: 74.5° on the left PFD, and 15.3° on the right one
- the left stick shaker was activated
- IAS and altitude disagree alerts were not recorded by the flight data recorder, FDR, but should have appeared on the PFDs; the disagrees themselves were recorded, though
- consequently, there was no conversation about IAS and altitude disagree and no non normal checklist was considered
- repeatedly, MCAS was triggered by the erroneous AOA values and caused the plane to pitch down
- at the third attempt, the pilots managed to engage the autopilot, even though its use is not foreseen in non normal situations, although it can reduce the workload
- at 05:39 and 23 seconds, slight rolls to the left and right, as well as slight heading deviations happened
The Unwanted Nosedives Continued
- at 05:39, flap retraction was started
- a few seconds later, the selected heading changed from 072° to 197°
- the autopilot disengaged
- the crew requested to maintain runway heading and reported "flight control problems" to ATC
- at 05:40, the flaps were fully retracted, and MCAS was activated
- following that, the ground proximity warning system, GPWS, alarmed the pilots: "don´t sink" and "pull up"
- at 05:40 and 22 seconds, the first officer asked the captain whether they should set the STAB TRIM switch to CUT-OUT, which the captain approved, and the switches were in the CUT-OUT position until 05:43:11
- during that time, the crew trimmed manually
- MCAS was active, but due to the switches in CUT-OUT position, the trimmable horizontal stabiliser, THS, did not respond to the inputs from MCAS
Increased Resistance in the Control Column and the Speed
- however, the resistance in the control columns was still huge, and both pilots pulled back their yokes applying much force, meaning that this mechanism against the alledged stall was still active
- when only one of the pilots pulled the yoke back, the plane would pitch down, when both pilots did so, a slight climb was possible
- at 05:41:21, the first officer called out "Captain! Speed", also the captain noticed that they were accelerating, but none of the pilots actually reduced the thrust, although the overspeed warning sounded
- at 05:42 and 47 seconds, the pilots reviewed existing faults and detected that the left alpha vane was dysfunctional
Reactivation of the STAB TRIM
- as the pilots had difficulties to trim the aeroplane manually, they enabled STAB TRIM again, which immediately also resulted in the MCAS commands being transmitted to the THS
- at 05:43 and 36 seconds, the GPWS warned: "terrain, terrain" and "pull up, pull up"
- with the last recorded values for airspeed: 500 knots, pitch value: > 40° nose down, and vertical speed values of 33 000 feet/minute, the recordings of both the CVR and the FDR stopped at 05:43 and 44 seconds
6. Important Results From Both Crash Investigations
The two crashes of a Boeing 737 MAX 8 happend within five months. Below, we will unveil the similarities, which were brought to light during the respective investigations (3,4), before exploring some of the additional contributing factors in both cases.
3) Komite Nasional Keselamatan Transportasi, Republic of Indonesia (201) Final, KNKT.18.10.35.04, PT. Lion Mentari Airlines, Boeing 737-8 (MAX); PK-LQP, Tanjung Karawang, West Java, Republic of Indonesia, 29 October 2018
4) The Federal Democratic Republic of Ethopia, Ministry of Transport and Logistics, Aircraft Accident Investigation Bureau (2022) Investigation Report on Accident to the B737-MAX8 Reg. ET-AVJ, Operated by Ethopian Airlines, 10 March, 2019
6.1. The Similarities Between the Two Boeing 737 MAX 8 Air Disasters
These include:
- erroneous values from the AOA sensors: flight LT 610 already during taxi, flight ET 302 immediately after lift-off
- the stick shaker was activated directly after lift-off
- several unwanted automatic aircraft nose down, AND, actions occured due to false values delivered by the AOA sensors
- a safe climb was not possible due to these AND commands
- the pilots´ workload was increased as they had to counteract each of these AND commands, which they had not initiated themselves
- the resistance in the control column increased, and the pilots experienced considerable difficulties as they pulled them aft
- the continuous fight against the AND commands also resulted in preocupation, stress, and a reduced overall situational awareness, all of which most likely have contributed to errors and omissions
- after only a few minutes into the flight, the aeroplanes went into a final, steep nosedive, from which no recovery was possible
- the jackscrew, which moves the horizontal stabiliser, was in the maximal nose-down position, which is in line with the steep dives
As MCAS was at that time automatically activated by the indicated angles from one single AOA sensor, the erroneous values from this sensor triggered the unwanted AND commands in both cases.
6.2. Other Contributing Factors
Other factors contributed to both Boeing 737 MAX 8 crashes. Below, we will concentrate on what was happening in the cockpits.
Flight LT 610:
- miscommunication between the two pilots
- PAN PAN PAN was not declared, this emergency code prompts air traffic controllers to prioritise the message
- no action was taken to stop the runaway stabiliser
- the crew, however, had searched the quick reference manual, but it could not find anything that explained the cause of their problem
Flight ET 302:
- no PAN PAN PAN was declared
- most likely due to preoccupation, the pilots forgot to reduce their airspeed
- following that, their speed increased until the crash, which also made it impossible to trim the stabiliser manually
- as the pilots could not trim their airliner manually, they enabled STAB TRIM again, which was a deviation from the standard operating procedures
- confusing alerts and the startle factor (final report, page 247)
7. Grounding of the Boeing 737 MAX 8, Effects, and Return to Service
7.1. The Grounding
After the crash of flight ET 302 on 10 March 2019, all Boeing 737 MAX 8 aircraft were grounded worldwide until December 2020. The first airline to ground them was Ethiopian Airlines, which did so on the day of the accident. The Chinese civil aviation authority followed the next day and grounded the planes of that type.
The FAA, however, chose to first issue a certificate of continued airworthiness before it grounded the aeroplanes on 13 March 2019. By 18 March 2019 all the 387 Boeing 737 MAX 8, which were in service around the world at that point in time, were grounded.
7.2. The Affected Airlines and Their Pilots
The affected airlines had to find the money to cover the tremendous costs as they, for instance, had to cancel flights, and reassign other aircraft to the flights they conducted. Several of them wanted Boeing to compensate for these financial losses. Pilots had to cope with a considerable amount of lost wages because of the cancelled flights.
7.3. The Effects on Boeing
Boeing faced lawsuits and investigations. In June 2019, the pilots, who had lost wages due to the groundigs, filed a joint class-action lawsuit against the manufacturer. In February 2020, the US Department of Justice investigated how Boeing had hidden the relevant details about MCAS from the FAA.
In January 2021, after having been charged with fraud, the company settled to pay more than 2.5 billion dollars. The sum also included payments to its customers, and the creation of a 500 million dollar beneficiary fund for the victims of the two crashes.
Boeing experienced a substantial loss of reputation and trust. It reported in January 2020 that customers had cancelled 183 orders for the Boeing 737 MAX 8. The company forfeited billions of dollars due to this loss of business alone.
7.4. The Boeing 737 MAX 8 Returned to Service in a Modified Version
The civil aviation authorities around the world allowed the Boeing 737 MAX 8 to return to service at different points in time. For example, the European Union Aviation Safety Agency, EASA, gave its approval to a modified version of the Boeing 737 MAX 8 in January 2021, mandating the following:
- appropriate pilot training
- a package of software updates
- rework of the electrical wiring
- updated operational manuals
- optimised maintenance
MCAS can now be overridden by the pilots.
8. What Can We Learn From the Boeing 737 MAX 8 Accidents?
We should observe carefully and reflect deeply when we read the facts about the two accidents and about how Boeing and the FAA acted prior to, but also in the aftermath of those. Then, we should think about how we can use at our work what we learned from each of the facets in these complex events.
For this, the following questions might provide us with guidance. There are no universal answers to them, as every single one of us encounters different working conditions.
What is our own attitude towards these facets of the Boeing 737 MAX 8 crashes? How do we decide to perform in our professional roles? In what work environment would we like to apply our knowledge and skills?
8.1. How Shall We Handle Automation?
As every work environment is different, the degree to which automation is used varies. Moreover, we might not have our say when new automated processes are introduced. However, everyone involved in the decision-making should carefully think about the necessity, the alternatives and what consequences malfunctions and outages may have.
We shouldn´t need to mention, that hidden systems are out of the question.
Every single one of us should also reflect on how to maintain his or her knowledge and skills in times of automation . Not only are they precious, we will also need them, when the technology all of a sudden is not available.
8.2. One Last Thought
Whenever we read press releases and other material about interactions between large companies of any type and the respective authorities, we should apply critical thinking. What information is given in the text and why? Where do we obtain more facts, especially about intentions, financial interests, and relationships?
In remembrance of the 346 victims, who lost their lives on the flights LT 610 and ET 302.
9. In the Next Article, We Will Explore CIRS in Medicine
What are critical incident reporting systems, CIRS? We will elucidate, who can report what to these systems, and how they are structured. What will follow after a report has been submitted? We will use established CIRS as examples and highlight how the reports are assessed and what recommendations are given. How shall we proceed when reading the cases in such a database?
Author: Eva-Maria Schottdorf
Date: August 31st, 2023
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