Opening the book…
This case study covers two crashes of Boeing 737 MAX 8 aircraft in late 2018 and early 2019, the subsequent grounding of all Boeing 737 MAX 8 aircraft, the analysis that was done to determine the root causes of the crashes, and recommendations for changes in order to re-certify the aircraft.
The case study will handle this as a quality issue with the project being the work required to attain FAA recertification.
This chapter will:
- Describe Boeing 737 model history
- Describe the circumstances of the two crashes
- Examine the National Transportation Safety Board (NTSB) recommendation to the the FAA
- Examine Federal Aviation Administration (FAA) actions
- Explore Congressional hearing material
- Explore project management considerations, especially quality analysis techniques
- Touch on legal considerations
Short History of the Boeing 737
Boeing’s 737 aircraft had been a dependable and successful aircraft since its development 50 years earlier. At the time of Boeing’s announcement to develop the new 737 MAX, it had delivered more than 9,000 of the 737 aircraft, in their various derivative models, since the first 737 had come off Boeing’s assembly line in 1967.[1, p40]
Producing a brand new aircraft would have been technically exciting and challenging, but the costs and time involved in doing so made Boeing’s executives anxious that they would lose out in competition to Airbus. After the decision was made to update the 737 and replace it with the new 737 MAX aircraft, an aggressive production schedule and cost-conscious measures targeting competing with Airbus played a major role in the program.
On March 8, 2017, the FAA granted an amended type certificate to Boeing for the 737-8 aircraft, the first of the 737 MAX family. The MAX is the 4th generation 737 model airplane and is the successor to the company’s 737 Next Generation (NG) family of aircraft. The 737 MAX was the 12th derivative model of the 737 aircraft, which was first certified half a century earlier in 1967.[1, p5]
In May 2017, the 737 MAX first entered revenue passenger service with Malindo Air, a Malaysian air carrier, two months after its FAA certification.[1, p5] Seventeen months later on October 29, 2018 the 737 MAX suffered its first fatal crash.[1,p5] The second crash occurred on March 10, 2019.
On March 12, 2019 international agencies began grounding the 737 MAX, followed by grounding by US authorities on March 13, 2019.
Flight Data Recorder
A flight recorder is an electronic recording device placed in an aircraft for the purpose of facilitating the investigation of aviation accidents and incidents. The device may be referred to colloquially as a "black box", an outdated name which has become a misnomer because they are required to be painted bright orange, to aid in their recovery after accidents.[7]
There are two types of flight recording devices: the flight data recorder (FDR) preserves the recent history of the flight by recording dozens of parameters collected several times per second; the cockpit voice recorder (CVR) preserves the recent history of the sounds in the cockpit, including the conversation of the pilots. The two devices may be combined into a single unit. Together, the FDR and CVR document the aircraft's flight history, which may assist in any later investigation.[7]
Figure \(\PageIndex{1}\): Cockpit voice recorder and flight data recorder, each with an underwater locator beacon on the front. (Public domain; By Dennis R. Grossi[7])
Two orange rectangular boxes each with an underwater locator beacon on the front.
Circumstances of the aircraft accidents
This section pulls material from NTSB Safety Recommendation Report ASR-19-01[3].
Lion Air Flight 610
On October 29, 2018, Lion Air flight 610, a Boeing 737 MAX 8, PK-LQP, crashed in the Java Sea shortly after takeoff from Soekarno-Hatta International Airport, Jakarta, Indonesia. The flight crew had communicated with air traffic control and indicated that they were having flight control and altitude issues before the airplane disappeared from radar. The flight was a scheduled domestic flight from Jakarta to Depati Amir Airport, Pangkal Pinang City, Bangka Belitung Islands Province, Indonesia. All 189 passengers and crew on board died, and the airplane was destroyed. The National Transportation Safety Committee of Indonesia took the lead on the investigation.
The airplane’s digital flight data recorder (DFDR) recorded a difference between the left and right angle of attack (AOA) sensors that was present during the entire accident flight; the left AOA sensor was indicating about 20° higher than the right AOA sensor. During rotation, the left (captain’s) stick shaker activated, and DFDR data showed that the left airspeed and altitude values disagreed with, and were lower than, the corresponding values from the right. The first officer asked a controller to confirm the altitude of the airplane and later also asked the speed as shown on the controller radar display. After the flaps were fully retracted, a 10-second automatic aircraft nose-down (AND) stabilizer trim input occurred. After the automatic AND stabilizer trim input, the flight crew used the stabilizer trim switches (located on the outboard side of each control wheel) and applied aircraft nose-up (ANU) electric trim. According to DFDR data, about 5 seconds after the completion of the pilot trim input, another automatic AND stabilizer trim input occurred. The crew applied ANU electric trim again. DFDR data then showed that the flaps were extended for almost 2 minutes. However, the flaps were then fully retracted, and automatic AND stabilizer trim inputs occurred more than 20 times over the next 6 minutes; the crew countered each input during this time using ANU electric trim. The last few automatic AND stabilizer trim inputs were not fully countered by the crew.
During the preceding Lion Air flight on the accident airplane with a different flight crew, the DFDR recorded the same difference between left and right AOA of about 20° that continued until the end of the recording. During rotation, the left control column stick shaker activated and continued for the entire flight, and DFDR data showed that the left airspeed and altitude values disagreed with, and were lower than, the corresponding values from the right. After the flaps were fully retracted, a 10-second automatic AND stabilizer trim input occurred, and the crew countered the input with an ANU electric trim input. After several automatic AND stabilizer trim inputs that were countered by pilot-commanded ANU electric trim inputs, the crew noticed that the airplane was automatically trimming AND. The captain moved the stabilizer trim cutout (STAB TRIM CUTOUT) switches to CUTOUT. He then moved them back to NORMAL, and the problem almost immediately reappeared. He moved the switches back to CUTOUT. He stated that the crew performed three non-normal checklists: Airspeed Unreliable, ALT DISAGREE (altitude disagree), and Runaway Stabilizer. The pilots continued the flight using manual trim until the end of the flight. Upon landing, the captain informed an engineer of IAS DISAGREE (indicated airspeed disagree) and ALT DISAGREE alerts, in addition to FEEL DIFF PRESS (feel differential pressure) light problems on the airplane.
On November 5, 2018, after evidence emerged of a potential contributor to the accident, the FAA conducted a preliminary risk assessment using the continued operation safety process established in FAA Order 8110.107A, Monitor Safety/Analyze Data (MSAD). Based on this risk assessment, the FAA determined urgent mandatory action was needed.[6,p6]
On November 6, 2018, the FAA issued a Continued Airworthiness Notification to the International Community (CANIC) (see Appendix D) to notify CAAs around the world that the FAA intended to issue an Emergency Airworthiness Directive (AD) to correct an unsafe condition on all 737 MAX aircraft. On November 7, 2018, the FAA issued Emergency AD 2018-23-51 (see Appendix C) requiring flight crews to use a revised runaway stabilizer operational procedure if they encountered certain conditions. The Emergency AD was an interim action, and further action was planned based on what the FAA and Boeing learned from investigating the JT610 accident.[6,p6]
Ethiopian Air Flight 302
On March 10, 2019, Ethiopian Airlines flight 302, a Boeing 737 MAX 8, Ethiopian registration ET-AVJ, crashed near Ejere, Ethiopia, shortly after takeoff from Addis Ababa Bole International Airport, Ethiopia. The flight was a scheduled international passenger flight from Addis Ababa to Jomo Kenyatta International Airport, Nairobi, Kenya. All 157 passengers and crew on board died, and the airplane was destroyed. The investigation is being led by the Ethiopia Accident Investigation Bureau.
The airplane’s DFDR data indicated that shortly after liftoff, the left (captain’s) AOA sensor data increased rapidly to 74.5° and was 59.2° higher than the right AOA sensor; the captain’s stick shaker activated. Concurrently, the airspeed and altitude values on the left side disagreed with, and were lower than, the corresponding values on the right side; in addition, DFDR data indicated a Master Caution alert. Similar to the Lion Air accident flight, a 9-second automatic AND stabilizer trim input occurred after flaps were retracted and while in manual flight (no autopilot). About 3 seconds after the AND stabilizer motion ended, using the stabilizer trim switches, the captain, who was the pilot flying, partially countered the AND stabilizer input by applying ANU electric trim. About 5 seconds after the completion of pilot trim input, another automatic AND stabilizer trim input occurred. The captain applied ANU electric trim and fully countered the second automatic AND stabilizer input; however, the airplane was not returned to a fully trimmed condition. Cockpit voice recorder data indicated that the flight crew then discussed the STAB TRIM CUTOUT switches, and shortly thereafter DFDR data were consistent with the STAB TRIM CUTOUT switches being moved to CUTOUT.
However, because the airplane remained in a nose-down out-of-trim condition, the crew was required to continue applying nose-up force to the control column to maintain level flight. About 32 seconds before impact, two momentary pilot-commanded electric ANU trim inputs and corresponding stabilizer movement were recorded, consistent with the STAB TRIM CUTOUT switches no longer being in CUTOUT. Five seconds after these short electric trim inputs, another automatic AND stabilizer trim input occurred, and the airplane began pitching nose down.
Partial data (e.g., altitude, airspeed and vertical speed) was available from a land-based Automatic Dependent Surveillance— Broadcast (ADS-B) system. On March 11, 2019, the FAA issued another CANIC (see Appendix D) indicating the FAA was actively involved in supporting the investigations. On March 11, the FAA received additional ADS-B data. The data was analyzed and reviewed on March 12 and through the early hours of March 13. Also on March 13, physical evidence from the crash site indicated that the aircraft was in a configuration that would have armed MCAS. The satellite ADS-B data from ET302, when compared with the Lion Air Flight Data Recorder (FDR) and physical data, indicated a potential causal link between the accidents. On March 13, with the potential relationship established between the two accidents, the FAA issued an Emergency Order of Prohibition (see Appendix A) grounding 737 MAX aircraft.[6,p6-7]
A common component in both of the airplane accidents was the new flight control feature: MCAS.[1,p11]
Maneuvering Characteristics Augmentation System
Boeing developed MCAS to address stability issues in certain flight conditions induced by the plane’s new, larger engines, and their relative placement on the 737 MAX aircraft compared to the position of the engines on the 737 NG.[1, p12]
The specifics of this are that the CFM International LEAP engine on the 737 MAX was larger and mounted further forward from the wing and higher off the ground than on previous generations of the 737. Boeing discovered that the aircraft engine had a tendency to push the aircraft's nose up when operating under certain conditions (flaps up, high angle of attack, manual flight). MCAS was intended to mimic the flight behavior of the previous Boeing 737 Next Generation (NG). Boeing indicated that this change eliminated the need for pilots to have simulator training on the 737 Max 8.[5]
MCAS was implemented to compensate for an excessive (high) angle of attack measured by an Angle of Attack (AOA) sensor by adjusting the elevators on the horizontal stabilizer near the airplane's tail before the aircraft would potentially stall. [5] The adjustment to the elevators should lift the tail and point the nose of the plane down.
Original Design Certification of the 737 Max 8
This section pulls material from NTSB Safety Recommendation Report ASR-19-01[3].
The 737 MAX 8 is a derivative of the 737-800 Next Generation (NG) model and is part of the 737 MAX family (737 MAX 7, 8, and 9).5 The 737 MAX incorporated the CFM LEAP-1B engine, which has a larger fan diameter and redesigned engine nacelle compared to engines installed on the 737 NG family. During the preliminary design stage of the 737 MAX, Boeing's testing and analysis revealed that the addition of the LEAP-1B engine and associated nacelle changes produced an ANU pitching moment when the airplane was operating at high AOA and mid Mach numbers. After studying various options for addressing this issue, Boeing implemented aerodynamic changes as well as a stability augmentation function, MCAS, as an extension of the existing speed trim system to improve aircraft handling characteristics and decrease pitch-up tendency at elevated AOA. As the development of the 737 MAX progressed, the MCAS function was expanded to low Mach numbers.[3, pp3-4]
A nacelle is an enclosed structure on an aircraft for an engine.
Figure \(\PageIndex{2}\): Angle of Attack Sensor. (Hannes Grobe - Own work, CC BY-SA 3.0[8])
An Angle of Attack (AOA) sensor adjusts itself to align with the direction of airflow sensed at the nose of the airplane. It reflects the angle of the airplane's wing relative to that airflow.
Both the 737 NG and the 737 MAX include a Speed Trim System that automatically moves the horizontal stabilizer in response to changes from trimmed airspeed while in manual flight for speed stability. The 737 MAX includes an additional pitch augmentation flight control law called MCAS, which affects pitch characteristics in manual flight, with flaps up and at elevated angles of attack, to compensate for the aerodynamic pitch effects associated with the 737 MAX’s larger, more forward located engines. MCAS enables the 737 MAX to comply with FAA regulatory requirements for certain handling qualities and cannot be removed unless replaced with a comparable system. Boeing has not presented a comparable system so the need for MCAS remains.[6]
The MCAS flight-control law is part of the Speed Trim System and is commanded by the FCC using data from sensors and other airplane systems. As a stability-augmentation system, MCAS automatically makes commands without pilot action. Either pilot can override MCAS commands to control the stabilizer by using the electric stabilizer trim switches on the control wheel. Additionally, flightcrews can set the STAB TRIM CUTOUT switches on the center control stand to CUTOUT to stop and disable MCAS.[6]
The MCAS flight-control law becomes active when the airplane exceeds an AOA threshold that varies depending on Mach (airspeed). If activated by a high AOA, MCAS moves the horizontal stabilizer at a rate of 0.27 degrees per second, which is the same trim rate as Speed Trim with flaps down. The magnitude of the MCAS command is a function of Mach and angle of attack. At higher airspeeds, flight-control surfaces are more effective than at lower airspeeds. Therefore, a smaller MCAS command at higher airspeeds has the same effect as a larger MCAS command at lower speeds. At low Mach, when the stabilizer has lower effectiveness, the MCAS command can be up to the maximum of 2.5 degrees of incremental stabilizer movement. The MCAS flight control law is reset after the AOA falls sufficiently below the AOA threshold.[6]
As originally delivered, the MCAS became active during manual flight (autopilot not engaged) when the flaps were fully retracted and the airplane’s AOA value (as measured by either AOA sensor) exceeded a threshold based on Mach number. When activated, the MCAS provided automatic trim commands to move the stabilizer AND. Once the AOA fell below the threshold, the MCAS would move the stabilizer ANU to the original position. At any time, the stabilizer inputs could be stopped or reversed by the pilots using their stabilizer trim switches. If the stabilizer trim switches were used by the pilots and the elevated AOA condition persisted, the MCAS would command another stabilizer AND trim input after 5 seconds.[3,p4]
The NTSB reviewed sections of Boeing’s system safety analysis for stabilizer trim control that pertained to MCAS on the 737 MAX. Boeing’s analysis included a summary of the functional hazard assessment findings for the 737 MAX stabilizer trim control system. For the normal flight envelope, Boeing identified and classified two hazards associated with “uncommanded MCAS” activation as “major.” One of these hazards, applicable to the MCAS function seen in these accidents, included uncommanded MCAS operation to maximum authority.10 Boeing indicated that, as part of the functional hazard assessment development, pilot assessments of MCAS-related hazards were conducted in an engineering flight simulator, including the uncommanded MCAS operation (stabilizer runaway) to the MCAS maximum authority.[3,p5]
To perform these simulator tests, Boeing induced a stabilizer trim input that would simulate the stabilizer moving at a rate and duration consistent with the MCAS function. Using this method to induce the hazard resulted in the following: motion of the stabilizer trim wheel, increased column forces, and indication that the airplane was moving nose down. Boeing indicated to the NTSB that this evaluation was focused on the pilot response to uncommanded MCAS operation, regardless of underlying cause. Thus, the specific failure modes that could lead to uncommanded MCAS activation (such as an erroneous high AOA input to the MCAS) were not simulated as part of these functional hazard assessment validation tests. As a result, additional flight deck effects (such as IAS DISAGREE and ALT DISAGREE alerts and stick shaker activation) resulting from the same underlying failure (for example, erroneous AOA) were not simulated and were not in the stabilizer trim safety assessment report reviewed by the NTSB.[3,p5]
MCAS Training and Documentation
“Boeing ultimately won the FAA’s approval to give pilots just an hour of training through an iPad about the differences between the MAX and the previous 737 generation. MCAS was not mentioned.”[2]
“The FAA, after internal deliberations, also agreed to keep MCAS out of the manual, reasoning that MCAS was a software code that operates in the background as part of the flight-control system...”[2]
NTSB Analysis: Assumptions about Pilot Recognition and Response in the Safety Assessment
On the Lion Air flight immediately before the accident flight and the Lion Air and Ethiopian Airlines accident flights, the DFDR recorded higher AOA sensor data on the left side than on the right (about 20° higher on the previous Lion Air flight and the Lion Air accident flight and about 59° higher on the Ethiopian Airlines accident flight). As previously stated, the MCAS becomes active when the airplane’s AOA exceeds a certain threshold. Thus, these erroneous AOA sensor inputs resulted in the MCAS activating on the accident flights and providing the automatic AND stabilizer trim inputs. The erroneous high AOA sensor input that caused the MCAS activation also caused several other alerts and indications for the flight crews. The stick shaker activated on both accident flights and the previous Lion Air flight. In addition, IAS DISAGREE and ALT DISAGREE alerts occurred on all three flights. Also, the Ethiopian Airlines flight crew received a Master Caution alert. Further, after the flaps were fully retracted, the unintended AND stabilizer inputs required the pilots to apply additional force to the columns to maintain the airplane’s climb attitude.[3,p7]
AND = Automatic Aircraft Nose Down
Multiple alerts and indications can increase pilots’ workload, and the combination of the alerts and indications did not trigger the accident pilots to immediately perform the runaway stabilizer procedure during the initial automatic AND stabilizer trim input. In all three flights, the pilot responses differed and did not match the assumptions of pilot responses to unintended MCAS operation on which Boeing based its hazard classifications within the safety assessment and that the FAA approved and used to ensure the design safely accommodates failures. Although a number of factors, including system design, training, operation, and the pilots’ previous experiences, can affect a human’s ability to recognize and take immediate, appropriate corrective actions for failure conditions, industry experts generally recognize that an aircraft system should be designed such that the consequences of any human error are limited.[3,p7]
Neither Boeing’s system safety assessment nor its simulator tests evaluated how the combined effect of alerts and indications might impact pilots’ recognition of which procedure(s) to prioritize in responding to an unintended MCAS operation caused by an erroneous AOA input.[3,p8]
Thus, the NTSB concluded that the assumptions that Boeing used in its functional hazard assessment of uncommanded MCAS function for the 737 MAX did not adequately consider and account for the impact that multiple flight deck alerts and indications could have on pilots’ responses to the hazard. Therefore, the NTSB recommended that the FAA require that Boeing:
- ensure that system safety assessments for the 737 MAX in which it assumed immediate and appropriate pilot corrective actions in response to uncommanded flight control inputs, from systems such as MCAS, consider the effect of all possible flight deck alerts and indications on pilot recognition and response; and
- incorporate design enhancements (including flight deck alerts and indications), pilot procedures, and/or training requirements, where needed, to minimize the potential for and safety impact of pilot actions that are inconsistent with manufacturer assumptions.[3,p8]
NTSB Analysis: System Diagnostic Tools
Multiple alerts and indications in the cockpit can increase pilots’ workload and can also make it more difficult to identify which procedure the pilots should conduct.[3, p10]
Human factors research has identified that, for non-normal conditions, such as those involving a system failure with multiple alerts, where there may be multiple flight crew actions required, providing pilots with understanding as to which actions must take priority is a critical need. This is particularly true in the case of functions implemented across multiple airplane systems because a failure in one system within highly integrated system architectures can present multiple alerts and indications to the flight crew as each interfacing system registers the failure. For example, the erroneous AOA output experienced during the two accident flights resulted in multiple alerts and indications to the flight crews, yet the crews lacked tools to identify the most effective response. Thus, it is important that system interactions and the flight deck interface be designed to help direct pilots to the highest priority action(s).[3, pp10-11]
Research demonstrates that emergency situations increase workload and require additional effort to manage effectively because of the stress involved and the lack of opportunity for pilots to practice these skills compared to those used in normal operations. In addition, research into pilot responses to multiple/simultaneous anomalous situations, along with data from accidents, indicates that multiple competing alerts may exceed available mental resources and narrow attentional focus leading to delayed or inadequately prioritized responses. According to FAA research, “in some airplanes, the complexity and variety of ancillary warnings and alerts associated with major system failures can make it difficult for the flightcrew to discern the primary failure.” The researchers noted that better system failure diagnostic tools are needed to resolve this issue.[3, p11]
Thus, the NTSB concludes that aircraft systems that can more clearly and concisely inform pilots of the highest priority actions when multiple flight deck alerts and indications are present would minimize confusion and help pilots respond most effectively. Therefore, the NTSB recommends that the FAA develop design standards, with the input of industry and human factors experts, for aircraft system diagnostic tools that improve the prioritization and clarity of failure indications (direct and indirect) presented to pilots to improve the timeliness and effectiveness of their response. The NTSB further recommends that once the design standards have been developed as recommended in Recommendation A-19-15, the FAA require implementation of system diagnostic tools on transport-category aircraft to improve the timeliness and effectiveness of pilots’ response when multiple flight deck alerts and indications are present.[3, p11]
NTSB Recommendations to the Federal Aviation Administration (FAA)[3, pp12-13]
Require that Boeing (1) ensure that system safety assessments for the 737 MAX in which it assumed immediate and appropriate pilot corrective actions in response to uncommanded flight control inputs, from systems such as the Maneuvering Characteristics Augmentation System, consider the effect of all possible flight deck alerts and indications on pilot recognition and response; and (2) incorporate design enhancements (including flight deck alerts and indications), pilot procedures, and/or training requirements, where needed, to minimize the potential for and safety impact of pilot actions that are inconsistent with manufacturer assumptions. (A-19-10)
Require that for all other US type-certificated transport-category airplanes, manufacturers (1) ensure that system safety assessments for which they assumed immediate and appropriate pilot corrective actions in response to uncommanded flight control inputs consider the effect of all possible flight deck alerts and indications on pilot recognition and response; and (2) incorporate design enhancements (including flight deck alerts and indications), pilot procedures, and/or training requirements, where needed, to minimize the potential for and safety impact of pilot actions that are inconsistent with manufacturer assumptions. (A-19-11)
Notify other international regulators that certify transport-category airplane type designs (for example, the European Union Aviation Safety Agency, Transport Canada, the National Civil Aviation Agency-Brazil, the Civil Aviation Administration of China, and the Russian Federal Air Transport Agency) of Recommendation A-19-11 and encourage them to evaluate its relevance to their processes and address any changes, if applicable. (A-19-12)
Develop robust tools and methods, with the input of industry and human factors experts, for use in validating assumptions about pilot recognition and response to safety-significant failure conditions as part of the design certification process. (A-19-13)
Once the tools and methods have been developed as recommended in Recommendation A-19-13, revise existing Federal Aviation Administration (FAA) regulations and guidance to incorporate their use and documentation as part of the design certification process, including re-examining the validity of pilot recognition and response assumptions permitted in existing FAA guidance. (A-19-14)
Develop design standards, with the input of industry and human factors experts, for aircraft system diagnostic tools that improve the prioritization and clarity of failure indications (direct and indirect) presented to pilots to improve the timeliness and effectiveness of their response. (A-19-15)
Once the design standards have been developed as recommended in Recommendation A-19-15, require implementation of system diagnostic tools on transport-category aircraft to improve the timeliness and effectiveness of pilots’ response when multiple flight deck alerts and indications are present. (A-19-16)
References
- Majority Staff of the Committee on Transportation and Infrastructure, Final Committee Report, The Design, Development & Certification of the Boeing 737 Max, September, 2020. Final Committee Report Boeing 737 Max.
- Dominic Gates and Mike Baker, “The inside story of MCAS: How Boeing’s 737 MAX system gained power and lost safeguards”, Seattle Times, June 22, 2019 and updated June 24, 2019. Seattle Times MCAS. Accessed March 27, 2026.
- NTSB Safety Report. National Transportation Safety Board. Safety Recommendation Report ASR-19-01. "Assumptions Used in the Safety Assessment Process and the Effects of Multiple Alerts and Indications on Pilot Performance", September 19, 2019. Accessed March 24, 2026.Official Report of the Special Committee to review the Federal Aviation Administration's Aircraft Certification Process, January 16, 2020.
- Wikipedia - MCAS. Accessed April 2, 2026. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.
- FAA, Summary of the FAA’s Review of the Boeing 737 MAX, Return to Service of the Boeing 737 MAX Aircraft, November 18, 2020. FAA Review of Boeing 737 Max. Accessed March 26, 2026.
- Wikipedia - Flight Recorder. Accessed April 6, 2026. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.
- Dennis R. Grossi. Public Domain, March 15, 2009. Image of Recorders.
- Hannes Grobe - Own work, CC BY-SA 3.0, AOA Sensor image.
6.1: Introduction is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by LibreTexts.
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