Implied and Expressed Meanings: Engineering Design,Embodiment,and Documentation for the 737 Max

Changes in Technology, Changes to the 737 Max

Of the 737 series, the Boeing 737-8 (MAX) is derivative of the 737-800 model and is part of the 737 MAX family (737 MAX 7, 8, and 9) (Final, 2019, p. 189). In the Max version, “it incorporated the CFM LEAP-1B engine, which has a larger fan diameter and redesigned engine nacelle compared to engines installed on the 737 Next Generation (NG) family” (Final, 2019, p. 189). Because the bigger engine was too close to the ground, it was moved forward for the sake of clearance. That in turn “produced an aircraft nose-up pitching moment when the aircraft was operating at high angles of attack (AOA) and mid Mach numbers. This nose-up pitching moment was deemed likely to affect the stick force . . . and the controllability and maneuverability requirements” (NTSB, 2019, p. 2). In situations where the angle of attack was too high and “the airplane approached the stall, the control forces — the necessary back pressure on the control column, did not increase in a conventional linear manner as they had in previous 737 s and as certification standards required” (Langewiesche, 2019).

The 737 included a speed trim system “to improve flight handling characteristics” (Final, 2019, p. 48), and Boeing installed the Maneuvering Characteristics Augmentation Software (MCAS) as an extension of the speed trim system [Final, 2019, p. 48] to push the nose down if the angle of attack were to cross a critical threshold. MCAS controlled the “large horizontal wing on the plane's tail known as the stabilizer, while the pilot controls smaller flaps or ‘elevators’ on the stabilizer” (Scot & Johnson, 2019). MCAS would operate

during manual, flaps-up flight (autopilot not engaged) when the AOA value received by the master FCC exceeded a threshold based on Mach number. When activated, the MCAS provided a high rate automatic trim command to move the stabilizer AND . The magnitude of the AND command was based on the AOA and the Mach. After the non-normal maneuver that resulted in the high AOA, and once the AOA fell below a reset threshold, MCAS would move the stabilizer ANU to the original position and reset the system. At any time, the stabilizer inputs could be stopped or reversed by the pilots using their yoke-mounted electric stabilizer trim switches, which also reset the system after a 5 second delay.

Of the three types of automation software—“static,” “adaptable,” and “adaptive” (Vogl et al., 2024, pp. 2–3)—MCAS was static automation except that, unlike the autopilot activated by the pilot, it would, without the pilot initiating it, turn itself on if the angle of attack sensor readings indicated too high an angle of attack. MCAS, though did not have the ability to discern if the angle of attack sensor readings were accurate or not and would automatically take control if the readings were too high.

Since Boeing and FAA test pilots also found out “that the MAX's controls didn’t stiffen as needed during certain lower-speed maneuvers, according to people familiar with the MCAS design” (Tangel et al., 2019), Boeing also provided “a desirable increase in stick force gradient and a reduced pitch up tendency” (Final, 2019, p. 48) and “quadrupled” (Tangel et al., 2019) the extent to which MCAS would act. In implementing MCAS software, Boeing had linked the operations of the MCAS to only one angle of attack sensor. Boeing viewed “the loss of one AOA and erroneous AOA as two independent events with distinct probabilities. The combined failure event probability was assessed as beyond extremely improbable, hence complying with the safety requirements for the Air Data System” (Final, 2019, p. 194).

Implied Meanings and Tacit Knowing, Expressed Meanings and Reflection

Implied meanings operating tacitly and generated by embodiment drive the exercise of skills. In the context of piloting, Langewiesche refers to such skills as follows: “The United States Navy manages to instill a sense of this in its fledgling fighter pilots by ramming them through rigorous classroom instruction and then requiring them to fly at bank angles without limits, including upside down” (Langewiesche, 2019). Because of the speed and complexity with which skills operate, they are exercised tacitly, based on implied meanings. Michael Polanyi, using Gestalt theory, explained that the exercise of skills happens in the tacit domain as humans integrate vast amounts of items at instantaneous speeds (Polanyi, 1966, p. 6), for creating meaningful outcomes. This integration of items is based on a from to structure, as one, at high speeds, integrates various items for forming meaningful actions. Because of the speeds at which these integrations occur, one is not aware of particular discrete actions (based on implied meanings or procedures), but they produce instantly meaningful whole actions constituted of vast numbers of discrete actions: “We identified the two terms of tacit knowing, the proximal and the distal, and recognized the way we attend from the first to the second, thus achieving an integration of the particulars to a coherent entity to which we are attending. Since we were not attending to the particulars themselves, we could not identify them” (Polanyi, 1966, p. 18). (That is why while writing instructions and procedures one needs to decompose phases of action in order to make visible the implied hidden meanings constituting those procedures.) Emphasizing this point concerning the speed of these integrations, Polanyi and Prosch in agreement with Lorenz say, “the speed and complexity of tacit integration far exceeds the operations of any explicit selection of supporting evidence” (Polanyi & Prosch, 1975, p. 42).

Hence, if one were to speak, one instantaneously and tacitly puts together sentences without consciously thinking about individual elements of sentences or hidden rules and procedures (implied meanings) based on which those sentences are generated tacitly below the threshold of consciousness. Because the rules are invoked tacitly below the threshold of consciousness, they are invisible, implied, and generated through embodiment at instantaneous speeds beyond the abilities of the conscious mind to process. In being experienced through bodily sensations, one knows the rules underlying the skill as an embodied sense. Such embodiment is generated through “indwelling” or dwelling in the skill through exercising it and experiencing the skill. The term Polanyi uses is “indwelling.”

As observers or manipulators of experience, we are guided by experience and pass through experience without experiencing it in itself. The conceptual framework by which we observe and manipulate things is present as a screen between ourselves and these things; their sights and sounds, and the smell and touch of them transpire but tenuously through this screen, which keeps us aloof from them. Contemplation dissolves the screen, stops our movement through experience, and pours us straight into experience; we cease to handle things and become immersed in them (Polanyi, 1962, p. 197).

When one, therefore, instantiates the skill domain through exercising it, one experiences and indwells the skill domain and becomes one with the world of that skill through developing an embodied sense of the skill and its underlying hidden rules (implied meanings). This embodied sense is in the form of unquantifiable sensations and feelings (that constitute the experience). Because these rules and procedures underlying the skill are implied and located in embodiment, they have been internalized tacitly and operate below the threshold of consciousness. One intuitively knows what procedures to follow without necessarily considering why one made those choices. The procedures themselves remain hidden, generated as an experience through embodiment and tacit knowing. For example, while swimming, as one instantiates the various rules of swimming experientially, this instantiation occurs at high speeds tacitly. While one is not consciously aware of all the particular rules operating as implied meanings and discrete movements of various swimming strokes, one experiences swimming as whole integrated body movements. One then has an unquantifiable embodied tacit sense of right and wrong for exercising the skill correctly.

Expressed meanings, on the other hand, are visible meanings extracted from practice and contained in documentation for communicating directly how the skill should be practiced. One, therefore, may know about the skill by having an understanding of expressed meaning through a conscious knowledge of the rules and procedures that define the skill; however, one knows the skill experientially through embodiment as one exercises it out of embodiment in the tacit domain based on implied meanings. Knowing a skill, therefore, based on implied meanings is fundamentally different from having conscious information about the skill as expressed meanings. Embodiment generates the knowing instantly, for operating at the high speeds necessary for adapting to the dynamic environments associated with the exercise of skills such as speaking, driving, flying, swimming, and so on.

In the context of skills involving technology, knowing the skill also means knowing experientially the technology as an embodied sense tacitly for exercising the skill. If it is a skill involving flying an airplane, the more one indwells the airplane by flying it or getting trained for flying it in a simulator, the more one develops an embodied experience of the airplane and knows the airplane experientially, and the more one knows the airplane experientially the more one will tacitly develop an embodied sense of how to fly the airplane based on its characteristics and rules and procedures based on those characteristics. Pilots will, therefore, have a corpus of implied meanings (rules and procedures) contained as embodiment tacitly driving their embodied sense of flying an airplane.

Expressed and Implied Meanings: Action-Reflection

One, though, cannot ignore expressed meanings. Expressed meanings constitute conscious knowledge of rules defining the skill and operate in the conscious domain. Although Polanyi does not discuss either embodiment or the conscious domain, without factoring in both conscious and tacit domains in relation to each other, one cannot fully understand the exercise of skills. Freud theorized the conscious domain (the ego) as the editor that enables people to consciously correct themselves and behave in socially appropriate ways (Freud et al., 1923, pp. 1–66). The conscious domain, therefore, supplies awareness of what is happening in the world, offers feedback over how to manage reality in the world, and, in the context of exercising skills, supplies an awareness of that experience. The exercise of skills is, therefore, not a blind exercise generated by embodiment out of the tacit domain because one has a sense of what one is doing and whether one is doing it correctly as a result of awareness supplied by the conscious domain.

Freud, on the other hand, did not theorize the tacit domain, nor did he examine categories of content that the conscious domain could process as opposed to content processed by the tacit domain. While the tacit domain is capable of processing unquantifiable content in the form of embodied knowing, the conscious domain can process expressed meanings as quantifiable information in the form of rules underlying skills. Because the conscious mind cannot process unquantifiable experiences, it also lacks the speed for using content in the form of quantifiable information for exercising skills. Instead, it can, through reflection, supply awareness for evaluating one's exercise of the skill and offer feedback on the implied meanings driving the exercise of skills tacitly. Hence, if a pilot has memory items for use while flying, such as the Non-Normal Checklist for a Runaway Stabilizer, because in this case memory recall involves recall of information, it is the conscious that enables the pilot to reflect on the nose-down movements of the airplane, recall those memory items, and use them in ways deemed safe.

Mixed Messaging: Older Expressed Meanings, Altered Implied Meanings

Because implied meanings are hidden and operate as an embodied experience out of the tacit domain, it is difficult to quickly verbalize and define the problem, something that needs to happen in the conscious domain. For the above reasons, a pilot says, during such moments, “You need some gut-level instinctive things to do to solve the problem” (Baker & Gates, 2019) with “gut level” functioning as another way of saying that pilots under such circumstances must know intuitively and tacitly what to do. In other words, it is a risk to change implied meanings because of the significant role they play in pilots’ exercise of skills.

Boeing used older expressed meanings (documented procedures) for a new technology on the premise that pilots will ignore changes to older implied meanings (tacitly exercised procedures) while following older expressed meanings. While introducing MCAS, Boeing merged the new MCAS software with the already preexistent speed trim system and presented any malfunctioning of the MCAS software as that of the speed trim system. The failure of this system would be a “runaway stabilizer” indicated by the movement of the trim wheels on the flight deck. The manual procedure for addressing a runaway stabilizer in the form of expressed meanings was “a trained flight crew memory item in 737- NG” [Final, 2019, p. 191] and was the same for the NG as follows:

• column input in the direction opposing the uncommanded trim until activation of the column-activated trim cutout switches, or

However, while the expressed meaning remained the same, the implied meanings (tacitly exercised procedures) had changed. In 737 models, including the NG, the column, just like cruise control on an automobile, included the yoke-jerk function that operates tacitly like the breaking system in an automobile for disengaging cruise control: “Much like tapping the brake pedal in a car to disengage cruise control, a sharp tug on the controls of older models of Boeing Co's 737 used to shut off an automatic trim system that keeps the plane flying level, giving the pilot control” (Scot & Johnson, 2019). However, “Boeing disabled the ‘yoke jerk’ function when it brought out the 737 MAX . . . and many pilots were unaware of the change” (Scot & Johnson, 2019).

Also, according to Swedish fighter pilot Fehrm, instructions from Boeing to American Airlines pilots following Lion Air 610's crash “emphasizes that pulling back the control column will not stop the action” [of MCAS] (Gates, 2018): “Pulling back on the column normally interrupts any electric stabilizer aircraft nose-down command, but for the 737-8 (MAX) with MCAS operating, that control column cutout function is disabled” (Final, 2019, p. 207). The report from Indonesia elaborates this change as follows:

On all 737 models, column cutout switches interrupt stabilizer commands, either from the autoflight system (e.g., FCC) or the electric trim switches in a direction opposite to elevator command. On the 737NG and MAX, two-column cutout switching modules, one for each control column, are actuated when the control columns are pushed or pulled away from zero (hands-off) column position. When actuated, the column cutout switching modules interrupt the electrical signals to the stabilizer trim motor that are in opposition to the elevator command.

Reinforcing changes to the column's functionality in the area of procedures were also other related changes that, being invisible, were unexpected and left pilots unprepared. “This nose-up pitching moment was deemed likely to affect the stick force . . . and the controllability and maneuverability requirements” (System, 2019, p. 2). Since Boeing had increased the column's backpressure and “quadrupled” (Tangel et al., 2019) the extent to which MCAS would act, that likely caught pilots by surprise as well.

MCAS-induced stabilizer movements were also different from stabilizer movements for a runaway stabilizer:

However, erroneous MCAS activation does not look like a typical stabilizer runaway, which is continuous un-commanded (runaway) movement of the stabilizer. During the accident flight, the stabilizer movement was not continuous; the MCAS commands were bounded by the MCAS authority (up to 2.5°); the pilots were able to counter the nose-down movement using opposing manual electric trim inputs; and after the pilots released the manual electric input and MCAS was reset, there was no other MCAS command for 5 seconds (Final, 2019, p. 197).

However, pilots were also expected to view these movements as well as those of a runaway stabilizer, which, in reality, they were not.

Implied Meanings and Embodiedness: An Unaddressed Gap

Since skills are based on embodiment while knowledge about the skill and the technology used for exercising the skill is in the form of information, there is a gap between knowing about the technology by acquiring information about the technology and knowing the technology by applying the rules for developing skills for controlling the technology. In order, therefore, for preventing such a gap developing between knowing about a skill and knowing the skill, one needs to experience in one's body through practice those procedures defining the skill for manipulating technology. Ideally, therefore, changes to hidden implied meanings, because they involve embodiedness operating out of tacit knowing, should begin with documentation followed by practice for internalizing those changes in the tacit domain and addressing the need to make changes to modes of thinking, muscle memory, and so on.

That can develop in users an embodied sense of the skill in the tacit domain and give “gut level” feelings that pilots of Ethiopian and Lion Air likely needed, but Boeing had, as a cost-saving measure, argued that simulator training was not needed for flying the Max. These pilots, for all practical purposes, had not experienced MCAS as an embodied sense. In the case of both Suneja and his First Officer, their training was almost entirely on 737 NG simulators or aircraft (Final, 2019, pp. 301–311), which significantly must have influenced their responses on their final flight. Suneja does not appear to have trained on the 737-8 Max (Final, 2019, p. 301) and Harvino had one “familiarization flight” (Final, 2019, p. 309). Hence, although pulling the column aft would not have helped, as Fehrm says, “Lion Air pilots would have trained on 737 simulators and would have learned over many years of experience that pulling back on the yoke stops any automatic tail maneuvers pushing the nose down.” Specifically referring to embodiment, Fehrm says, “It fits in your feel memory” which is “a physical way of learning” and asserts, “the pilots would have pulled back and found the downward nose movement didn’t stop” (Gates, 2018).

Neither is there, though, any clear evidence that either Getachew or his First Officer, Mohammed, was able to train on a 737 Max simulator or had detailed documentation for managing manual procedures while experiencing MCAS. Although Ethiopian had a 737 Max simulator, the New York Times claims that Getachew did not train on it and was not due for his next training period until after the accident flight (Ducharme, 2019). While Ethiopian Air has criticized this observation, the New York Times says that it stands by its position and nothing in Ethiopian Air's criticism addresses the point that Getachew did not train on a 737 Max simulator (Gebrekidan, 2019). The above point, combined with the observation by Ethiopian Air “that the 737 MAX flight simulator was not designed to include problems with the new plane's automated systems, which are suspected of contributing to the crash” (Ducharme, 2019), indicates that even if Getachew and Mohammed, his first officer, had had a chance to train on the simulator, they would not have had an opportunity to test MCAS-related scenarios: As “whistleblower from Ethiopian, veteran pilot Bernd Kai von Hoesslin, told the AP in May that after Indonesia's Lion Air crash, he pleaded with Ethiopian's top executives to give pilots better training on the Max, predicting that if pilots are not sufficiently drilled on Boeing's protocols for how to disable the autopilot system in the event of a misfire, ‘it will be a crash for sure’” (Wasson, 2019).

Usability Principles and Altered Implied Meanings

Usability has a role to play in pilot performance and workload (Williams & Ball, 2004). Because usability involves the relationship between the machine and the human, it has a bearing on the exercise of skills. When, therefore, hidden implied meanings are altered, that can violate usability principles and have a bearing on the exercise of skills. Boeing, while expecting pilots to act based on prior training involving earlier expressed meanings, operated on the premise that altered implied meanings would not pose problems. In its marketing as well, Boeing had pointed out that pilots did not need simulator training for transitioning to the Max from other 737 models: “Minimizing MAX pilot transition training was an important cost saving for Boeing's airline customers, a key selling point for the jet, which has racked up more than 5,000 orders” (Gates, 2019a). It was not required for “experienced 737 pilots to do any additional learning in a simulator” (Browning, 2019). On its website, the company had also indicated savings of “millions of dollars” as a result of being similar to the 737 NG (Gates, 2019a). Dennis Tajer, a spokesman for the Allied Pilots Association at American Airlines, said “his training on moving from the old 737 NG model cockpit to the new 737 MAX consisted of little more than a one-hour session on an iPad, with no simulator training” (Gates, 2019a).

Related to the above assumptions was also the other assumption that one need not know why something is happening: “As pilots we really don’t need to know why the trim is running away, but we must know, and practice, how to disable it” (Browning, 2019). Similarly, pilots of United Airlines also observed that well-trained pilots should be able to “diagnose the problem” even if they were not aware of the existence of the MCAS, as was the case on the flight prior to Lion Air 610 and Lion Air 610 (Lahiri, 2019). In keeping with this view, a Boeing official also in a Q&A with pilots asked, “If there are three or four or five things that could cause a runaway stabilizer, why do you need to know which one it is before you operate the procedure” (Tangel et al., 2019).

These changes involving hidden meanings violated the fundamental usability principle of consistency: “similar tasks should be performed in similar ways” (Jordan, 2002, p. 25). It also “refers to design regularities within a product or across a range of particular product types” (Jordan, 2002, p. 26). These changes in hidden implied meanings, in remaining hidden, also violated the foundational usability principle also referred to as “explicitness” with “products . . . designed so that it is clear how to operate them” (Jordan, 2002, p. 37). All the above violations, in turn, negatively impacted another usability criterion: “experienced user performance (EUP),” “the relatively unchanging performance of someone who has used a product many times before to perform particular tasks” (Jordan, 2002, p. 13). Instead of being an asset “EUP” becomes a liability as pilots were prone to operating based on erroneous implied meanings from the past. Those past experiences did not produce the desired outcomes and led to ineffective actions.

A case in point are changes to the column. It effectively serves as a conduit for receiving sensory feedback from the airplane and enables the pilot to respond based on embodiment for directing the airplane. Just as an automobile's steering wheel, connected, in turn, to the wheel assembly through a column, easily enables the driver to sense the automobile's handling of the road through sensations transmitted through the steering wheel, the pilot receives, through the column, feedback in an embodied sense from the airplane and enables the pilot to know the airplane. Pressures on the airplane's external surfaces, such as those from the tail assembly, the wings, and so on, are synthesized as a holistic experience of an object moving in space communicated through forces felt through the column. Easy mapping (Norman, 2002, p. 23) makes it easy for the pilot to correlate up and down pitch movements with forward and aft movements of the column, similar to the movements of a steering wheel, where easy mapping enables the driver to easily correlate the movements of the wheel with that of the car. The column, therefore, as an intuitive control, quickly enters the tacit domain and serves as a tool for pilots to develop an embodied sense of the airplane and indwell it as a flying object.

Changes to the column involving hidden implied procedural meanings, therefore, as per reports, were generally invisible and did not meet usability standards of visibility. As Fehrm, speaking as a fighter jet pilot, says, “Any pilot's natural reaction when a plane's nose begins to tilt down uncommanded is to pull back on the yoke and raise the nose. In normal flight mode, that would work, because pulling back on the yoke triggers breakout switches that stop any automatic tail movement tending to move the nose of the plane down. But with the MCAS activated . . . those breakout switches wouldn’t work. MCAS assumes the yoke is already aggressively pulled back and won’t allow further pullback to counter its action, which is to hold the nose down” (Gates, 2018).

As reported, “The 737 MAX can fly without MCAS, so the feature was not considered ‘flight-critical’ even though it has extraordinary power to steer the plane” (Scot & Johnson, 2019). The MCAS software itself would not activate if the flaps were extended. Boeing did not anticipate a problem and rated the system for hazardous, not catastrophic outcomes: “Boeing concluded that the effect would be hazardous until the flight crew recognized the problem and took appropriate action to mitigate it” (Final, 2019, p. 195). However, pilots were generally unaware of this change, and this change was not visible. Lack of visibility led to problems with usability principles of consistency, learnability, and guessability, and turned “experienced user performance” into a liability. “Consistency means that similar tasks should be performed in similar ways. This will mean that as a user gains experience with a product, he or she can generalize from what has been learned when performing one task with the product to help achieve another” (Jordan, 2002, p. 25). Changing the column's functionality counterintuitively in certain areas of the flight envelope and letting that remain hidden affected “learnability” which “can be particularly important in situations where training time is short or a user is to be self-taught with a product” (Jordan 12) as was the case with the 737 Max. That in turn could affect the usability principle of “experienced user performance”. Experienced pilots may find it startling that a commonly used procedure was not working because it was operational only at certain times in certain areas of the flight envelope and, instead of learning, could be confused, startled, and wonder about the nature of the problem because, in reality, they were not dealing with a stabilizer acting on its own but the controlled movements of a stabilizer erroneously directed by MCAS.

It is similarly the case with the column's backpressure, which violates usability principles of visibility and easy ergonomics. “Column forces exceeded over 100 lbs., which is more than the 75 lbs set by regulation (14 FAR 25.143)” (Final, 2019, p. 196). Pilots, therefore, operated based on implied meanings that stick force would be reasonable and would be appropriate to use despite any mistrim. However, “during the accident Lion Air flight, the DFDR recorded a control force of 103 lbs., after repetitive MCAS activation . . . . At this point, the flight crew was unable to maintain altitude” (Final, 2019, p. 228). Even on Lion Air 1043, the flight before Lion Air 601, “The FO commented that the aircraft is “too heavy to hold back” (Final, 2019, p. 175). In simulator tests as well, following “two full applications of MCAS and no restoring electric manual trim up,” one participant characterized the control column force as “too heavy” (Final, 2019, p. 95). If pilots were unaware of this change, they could have thought something was fundamentally wrong and could have become confused. According to “flight control experts,” “the new system kicking in would have changed the feel of the plane's control yoke from what the pilots had experienced training on simulators, possibly sowing confusion aboard Flight JT610” (Gates, 2018).

Aggravating the confusion, such backpressure, in increasing the weight, violated usability principles of ergonomic ease of use and made it cognitively difficult to troubleshoot: As aviation consultant Doug Moss puts it, “When you’re pulling on the column with 80-100 pounds of force trying to save your life, your troubleshooting techniques are very weak” (Baker & Gates, 2019). This change concerning backpressure was invisible because pilots of Lion Air and Ethiopian, operating off past implied meanings, did not appear to know that MCAS nose-down movements if not appropriately taken care of, following two MCAS-induced movements could be catastrophic: “If one of these three flight crew trim responses is not used, a subsequent combination of MCAS commands and short-duration (insufficient) flight crew electric trim inputs may result in a mis-trimmed condition that cannot be controlled” (Final, 2019, pp. 193–194).

Lack of visibility, in turn, produced more usability issues. Donald Norman argues that in order to use a product and its controls well, one should have an understanding of the system's operations (Norman, 2002, pp. 12-13). However, MCAS induced stabilizer movements were different from stabilizer movements of a runaway stabilizer, which kept Lion Air pilots from developing an understanding of the operations of the system. In the case of Ethiopian Air, they had a partial understanding of the system. They recognized MCAS-induced movements and operated based on the implied meaning that manual documentation would work. They did not, though, fully understand how the stabilizer as a part of the tail assembly would respond under pressure from extreme forces. Under certain conditions, the stabilizer could get stuck, and Ethiopian Air's flight crew could have benefited from technical documentation in the form of additional procedures and warnings concerning the use of manual procedures in case they did not work.

Mixed Messaging: Disrupting the Balance, Missing Documentation

Pilots have personality traits (Chapparo et al., 2020), and their cognition cannot be viewed in isolation from their psychological states. Both “surprise” and “startle” effects can produce psychological states that can impact pilot performance. “Surprise” is a “cognitive-emotional response” and is of longer duration than “startle.” “Startle,” on the other hand, “is defined as a sudden involuntary reaction to an intense stimulus” (Vlaskamp et al., 2025). Research also by “researchers agree that the way people make time pressured decisions is not via a process of generating internal probabilities and comparing rational option sets” (Tuccio, 2011, p. 40). It has also been noted that when pilots experience the “startle response” that “evokes a reflexive action . . . counter to the proper response” (Tuccio, 2011, p. 40). The above happens because surprise and startle can result in a lack of clarity, which, in turn, can release emotions of anxiety over questions of how to proceed. Since anxiety is a form of embodiment and, hence, processed in the tacit domain, a better understanding of the relationship between the conscious and tacit domains may enable pilots to receive feedback, reflect, and avoid confusion by having a balanced relationship between those domains. While surprise and the “startle” effect can disrupt this balance and create confusion, when the conscious and tacit domains are in a balanced relationship, they will be able to interact in such a way that the conscious domain is able to give the pilot feedback on actions generated out of the tacit domain. With a balanced relationship between both domains, pilots may have an action-reflection loop where they exercise skills, reflect and receive feedback while doing so, and respond with a clear sense of what to do and how to do it. They could do that by checking altitude, airspeed, and so on, and, if needed, use information concerning those variables for deciding how to proceed.

Anxiety, though, because it is a form of embodiment, as are implied meanings—which also operate out of embodiment—while different from implied meanings operating tacitly and experientially, in being unquantifiable and belonging to the larger category of embodied experience, do not have firewalls separating them. As a result, anxieties over the correct procedures to follow while exercising skills can mix with embodiment driving the exercise of skills and impact the exercise of skills. Without the firewalls that exist between the conscious domain containing information and the tacit domain containing embodiment anxieties in the form of strong emotions can make the operations of the tacit domain stronger and, in doing so, may crowd out the conscious domain and keep it from offering feedback. At such times, pilots may operate primarily based on embodiment, tacit knowing, and implied meanings out of a low threshold of consciousness without much awareness of their actions and with little or no reflection or feedback from the conscious domain for future course of action. Following is a description of such a state of mind: “It's terrifying for a pilot to struggle to control his airplane, and the surge of intense fear makes it impossible to think creatively, an effect psychologists call ‘cognitive tunneling’” (Wise, 2019).

Pilots flying the Max, therefore, with little or no documentation in the form of expressed meanings and no simulator training, were receiving mixed messages. While on the one hand, they were given the impression that nothing had changed when certain fundamental functionalities, procedures, and ways in which the airplane would behave as a result of MCAS had changed, the expectation was that pilots would use unchanged expressed meanings from the past for manually controlling the stabilizer, but not attempt to operate off implied meanings from the past that had changed. If they did, they likely would be taken by surprise and possibly experience the “startle” effect—which likely is what happened. In Suneja and Harvino's case, they did not know about MCAS, while Getachew and Mohammed, although they knew about MCAS, from how they responded, were taken by surprise as well at different moments.

Both flight crews responded based on past implied meanings. Boeing could have preempted that by offering technical documentation as expressed meanings in the form of warnings that MCAS-induced nose-down movement may not look like nose-down movements as a result of a runaway stabilizer, but the procedure to use for addressing either one was the one for manually controlling a runaway stabilizer. That would have addressed changes to the implied meanings of how MCAS-induced stabilizer movements would look. Similarly, pilots could have been issued documentation in the form of warnings as well about the possibility of the stabilizer getting stuck, with extra emphasis on the need to use the electric switches before moving to manual procedures, and some modified procedures in case the stabilizer still refused to respond. That again would have addressed implied meanings that the use of manual procedures would be a straightforward simple affair.

Human Factors and Implied Meanings

Extraneous human factors can also potentially aggravate the possibilities for implied meanings to generate confusion in the cockpit. The airline industry is a global industry that covers a wide range of cultures and practices in a rather uneven manner. In the case of Lion Air 610, neither pilot should have flown that morning. As per the recording of the conversation on the flight deck, the captain is heard saying that he had the flu and coughed 15 times before the flight. The First Officer is recorded saying that he was not on the schedule but was woken up at 4.00 am (Final, 2019, p. 79) for a flight leaving early in the morning. Similarly, the First Officer's inadequate use of the electric switches brings up the issue of training because he had had aircraft handling problems that were not addressed in training: “The reappearance of difficulty in aircraft handling identified during training in the accident flight indicated that the Lion Air training rehearsal was not effective” (Final, 2019, p. 212).

Also, the captain was originally from India, while his first officer was from Indonesia. One wonders if there were communication gaps due to culture, because the captain did not give the First Officer clear directions when handing over control, and the First Officer did not complete the captain's request for checking the Non-Normal airspeed checklist. Nor did the First Officer use the electric switches appropriately. Maybe better instructions in the form of technical documentation concerning confusing changes to procedures underlying implied meanings could have overridden human factors and better prepared the crew to deal with the unexpected and communicate better as well. In the case of Ethiopian, while the captain had 8000 or so hours of flying, his First Officer had around 150 hours. One wonders, considering the relative lack of experience of the First Officer, if more documentation in the form of expressed meanings could have made a difference.

Lack of Meaning: Suneja and Harvino

If the conscious mind does not supply feedback, it can lead to confusion and loss of meaning. Boeing's expectation for diagnosing the situation was 4 seconds (Tangel et al., 2019), and for Langewiesche, an experienced pilot, it was 30 (Langewiesche, 2019); however, Lion Air 1043's “flight crew required 3 minutes and 40 seconds” (Final, 2019, p. 193) and that too through feedback from a pilot catching a ride (Langewieshe, 2019) “during which repetitive uncommanded MCAS activations occurred” (Final, 2019, p. 193). In Suneja's case until the end, he did not diagnose the problem. (The checklist for a runaway stabilizer was a memory item and memory involves recalling information. In order, therefore, to activate one's memory one needs the operations of the conscious.)

Confronted with a lack of meaning and likely experiencing anxiety over why the column or the electric switches did not solve the problem permanently, Suneja appeared to operate mainly out of the tacit domain without much reflection from the conscious mind. He repeatedly responded based on ineffective implied meanings, something expected in such situations: “decision makers use categorization of prior experience to solve new problems, often including rapid mental stimulation of outcomes” (Tuccio, 2011, p. 41). When MCAS activated on both Lion Air 610 and also on the previous flight (Lion Air 1043), both flight crews, responding tacitly based on implied meanings contained in embodiment, from past experiences relied on the column as a control at critical moments to relieve the situation: “by pulling back on the control column” (Final, 2019, p. 192). Describing Suneja's intuitive responses, “For the first MCAS activation in the accident flight, the Captain responded less than 2 seconds, with aft control column but MCAS continued to move the horizontal stabilizer AND for a total of 10 seconds, after which the Captain applied electric trim” (Final, 2019, p. 191). The accident report from Indonesia as well points out, “Review of the DFDR data showed that both during the accident and the previous LN I043 flights, the flight crew responded within 2-3 seconds using control column to control the flight path and subsequently trimmed out column forces using electric trim” (Final, 2019, p. 193).

The fact that the column's functionality had changed during MCAS operations must have confused the flight crew. Not knowing about MCAS either, when it kicked in because of erroneous data from a faulty angle of attack sensor, Suneja likely did not connect nose-down movements to a runaway stabilizer, maybe because MCAS-induced stabilizer movements, as mentioned earlier, looked different from the “continuous” movements of a runaway stabilizer. That may explain why he repeatedly fell back on the electric switches, although they stopped the problem only temporarily.

On the Lion Air flight, when the MCAS pushed the jet's nose down, the captain pulled it back up, using thumb switches on the control column. Still operating under the false angle-of-attack reading, MCAS kicked in each time to swivel the horizontal tail and push the nose down again.

The black box data released in the preliminary investigation report shows that after this cycle was repeated 21 times, the plane's captain ceded control to the first officer. As MCAS pushed the nose down two or three times more, the first officer responded with only two short flicks of the thumb switches (Gates, 2019a).

Following the use of the electric switches, Suneja kept falling back on the column although it did not solve the problem.

Even if, therefore, Suneja had realized that the AOA sensor was supplying false data—which he did not—it may not have helped because that did not explain why the nose was being pushed down. Operating strongly out of the tacit domain, he did not recall the memory item for a runaway stabilizer either. Instead, Suneja asked First Officer Harvino to check the Non-Normal Airspeed checklist which Harvino was not able to provide immediately: “The inability for the FO to perform memory items and locate the checklist in the QRH in a timely manner indicated that the FO was not familiar with the NNC [Non Normal checklist]. This condition was reappearance of misidentifying NNC which showed on the FO's training records” (Final, 2019, p. 212).

Operating tacitly out of a low threshold of consciousness, Suneja did not make different cause-and-effect correlations if he had reflected with feedback from the conscious. Not only did he not notice the switches before him for shutting down the electric motor driving the stabilizer or the large trim wheels next to him as it moved with the movements of the stabilizer, he also did not correlate MCAS-induced nose-down movements with the movement of the flaps on the wings. MCAS would activate only when the extended flaps on the wings were retracted. Suneja could have extended the flaps and landed the airplane if he had made cause-and-effect connections and correlated those movements (Langewiesche, 2019).

Suneja's First Officer Harvino, also likely experiencing high levels of anxiety over the possibility of something having gone wrong irrevocably, appears to have frozen and shut out the conscious mind completely. Suneja had asked him to use the electric switches to trim the airplane, but the electric trim inputs he gave were insufficient: “He gave a few feeble inputs of nose-up trim with his thumb switch and began calling on God for a miracle” (Langewiesche, 2019). Both pilots, in operating based on erroneous implied meanings concerning the technology, did not realize that a mistrim if not addressed immediately, could lead to MCAS resets that could be catastrophic.

Incomplete Meanings, Implied Meanings: Getachew and Mohammed

In the case of Ethiopian 302, the flight crew knew about MCAS, but without more detailed documentation, their behavior, in relying on the column at critical moments, appears to indicate they were not aware of changes to implied meanings concerning the column's functionality. In their case as well, their response was delayed when MCAS kicked in, and in a 6 minute flight, it took Getachew and Mohammed four minutes to diagnose the problem. Operating based on implied meanings without much feedback from the conscious domain, just like the flight crews of Lion Air 610 and Lion Air 1043, when MCAS kicked in the first time, both pilots, responded, “immediately by pulling back on their control yokes” (Wise, 2019).

Once they realized the problem was MCAS induced, again operating based on the implied meaning that the author is omniscient and written procedures offered as expressed meanings will work, Getachew and Mohammed attempted to use the trim wheels for manually controlling the stabilizer and, in their eagerness, hardly used the electric switches to activate the powerful motor for controlling the movements of a runaway stabilizer. While it is reported that the pilots used “a switch on their yokes to trim the stabilizer back up” (Wise, 2019), Dominic Gates, The Seattle Times correspondent, referring to this moment says, they

jumped straight to the end of the procedure checklist and hit the cut-off switches before attempting even to counter the nose-down movement with the thumb switches on the control column. That would have subjected them almost immediately to the high tail forces that could have made recovery impossible (Gates, 2019b)

At the same time Getachew, again possibly overwhelmed with anxiety, without much feedback from the conscious mind, had not “throttled back from full take off settings” and the airplane “in level flight was going extremely fast, 25 knots faster than the maximum operating speed of 340 knots, and was rapidly accelerating into realms beyond the flight-testing range” (Langewiesche, 2019). In making very little use of the powerful electric motor, the flight crew were also operating based on the premise which implied that manual procedures would work if pilots were to straightforwardly follow those procedures. However, the stabilizer, likely as a result of overspeeding, was subject to high physical forces and had jammed the jackscrew operating it.

Some documentation in the form of warnings or additional procedures anticipating how the stabilizer could behave under the influence of high forces could have addressed the usability issues coming out of the implied meanings and expectations of the procedures working straightforwardly. Especially considering that Mohammed and Getachew, without much thought, jumped to the manual procedure—almost skipping the use of electric switches, the documentation could have deliberately, in the form of a warning, emphasized the need to use the electric switches before using manual procedures and pointed out the risks of a stuck stabilizer if electric switches were not used before trying to control the stabilizer manually: “The bottom of Boeing's runaway stabilizer checklist seems to acknowledge the possibility of this physically challenging scenario. It suggests that the pilots can first use the electric trim to neutralize those potential forces before hitting the cutout switches” (Baker and Gates, 2019). Boeing could have, in addition, adapted instructions offered in a 1982 manual for situations where aerodynamic forces may make it difficult to manually raise the airplane's nose. These procedures, operating in a “counterintuitive” manner, prepared pilots of, for instance, the 707 in the 1950s and 1960s, but “in the later 737 models that followed the -200, what was called a ‘runaway stabilizer' ceased to be a problem’ (Gates, 2019b). Referred to as the “roller coaster technique,” according to the manual, “If nose-up trim is required, raise the nose well above the horizon with elevator control. Then slowly relax the control column pressure and manually trim nose-up. Allow the nose to drop below the horizon while trimming (manually). Repeat this sequence until the airplane is trim” (Gates, 2019b). (Just as in the case of the crew of Lion Air 610, the crew of Ethiopian 302 did not correlate nose-down movements with the movement of the flaps. Both flight crews could have extended the flaps and landed the airplane if they had made cause-and-effect connections and correlated these movements.)

No Meaning, A Procedural Cul de Sac

When implied meanings do not work, pilots operating out of the tacit domain without much feedback from the conscious, not seeing any new options, may fall back on known procedures even repeatedly when they have already been ineffective or erroneous. Violations of usability principles such as visibility and consistency may trigger these mistakes. If on some occasions the column worked and on some occasions it did not, that would be inconsistent feedback that would be confusing. When, therefore, Suneja took control back from Harvino, he tried to use the column again and pull aft without success: “Suneja hauled his control column all the way back, giving full up elevator to no avail. The nose dropped farther as the stabilizer prevailed. The crew of an offshore oil platform saw the airplane in a nearly vertical dive before it hit the water” (Langewiesche, 2019) at “more than 500 miles an hour” (Gates, 2019a). In the case of Ethiopian 302, with manual procedures not working, the flight crew tried erroneous procedures: First Officer “Mohammed flipped the cutout switches to reactivate the electric trim, but apparently less to use the thumb switch — Getachew gave it two halfhearted tries — than to activate the autopilot as a way of disabling the MCAS. The record shows four attempts in rapid succession to engage the autopilot, all of which were refused because autopilots are not recovery devices and will not engage if they sense pressures on the control column” (Langewiesche, 2019).

Based on past implied but ineffective meanings, Getachew relied on the column as well (Bremmer, 2019). The stabilizer remained stuck aggravated by the overspeeding which very likely introduced high physical forces on the stabilizer and jammed the jackscrew operating the stabilizer: “Investigators also found the Ethiopian plane's jackscrew, a part that moves the horizontal tail of the aircraft, and it indicated that the jet's horizontal tail was in an unusual position — with MCAS as one possible reason for that” (Gates, 2019a). With the autopilot not working, Getachew once again used the column: “The airplane was now so far out of trim that Getachew had to hold his control column halfway back (meaning half up-elevator) to keep the nose from dropping” (Langewiesche, 2019). Because of the pressure he “was muscling his control column halfway back.” Getachew then let go of the column in the hope that letting go would let the autopilot take over. When the autopilot would not engage, once again, responding tacitly, he pulled the column aft while “the MCAS kicked in and achieved full nose-down trim, doubling the angle of the dive. As the speed shot through 450 knots, the pilots hauled back on their control columns to no effect” (Langewiesche, 2019).

Some expressed meanings as documentation in the form of warnings concerning changes to the column's functionality, including in the form of warnings on increasing stick force, may have prepared the flight crew. If one has to focus on the heavy column, there is hardly any headspace for anything else. Getachew “for minutes” was “using brute physical force to pull the control yoke back in order to keep the plane's nose from sinking,” work described as “exhausting” and not “endlessly” possible (Wise, 2019). As a result, he must have felt like riding a “roller coaster” (Wise, 2019).