Boeing 737 MAX MCAS: a flight-control function acts on a single sensor, repeatedly and without pilot command; Lion Air 610 (29 Oct 2018) and Ethiopian 302 (10 Mar 2019)
The typed evidence object. This is the working store; the case page is the reader's form.
| Layer / facet | Value | Type | Sources | Conf. |
|---|---|---|---|---|
| Mandate: principal | Boeing, as designer; the operating airlines as principals in service | fact | House Committee on Transportation and Infrastructure (majority staff), Final Committee Report: The Design, Development and Certification of the Boeing 737 MAX | high |
| Mandate: objective | Compensate for pitch-up handling at high angle of attack, consistent with the program's directive to avoid pilot simulator training requirements | fact | House Committee on Transportation and Infrastructure (majority staff), Final Committee Report: The Design, Development and Certification of the Boeing 737 MAX; Komite Nasional Keselamatan Transportasi (KNKT), Aircraft Accident Investigation Report, PT. Lion Mentari Airlines Boeing 737-8 (MAX) PK-LQP, Tanjung Karawang, West Java, 29 October 2018 | high |
| Mandate: disclosed to supervisor | Boeing, with FAA approval, removed references to MCAS from the flight crew operations manual and training materials; pilots were largely unaware of it. The deferred prosecution agreement records that two Boeing technical pilots deceived the FAA group that set pilot training requirements about MCAS, while others at Boeing disclosed its expanded scope to the FAA staff who assessed airworthiness. After the Lion Air crash, a Boeing bulletin (6 November 2018) and an FAA emergency airworthiness directive (7 November) warned of repeated nose-down trim from an erroneous angle-of-attack reading without naming MCAS, and on 10 November 2018 Boeing described MCAS in a message to airlines flying the MAX, including Ethiopian Airlines | fact | House Committee on Transportation and Infrastructure (majority staff), Final Committee Report: The Design, Development and Certification of the Boeing 737 MAX; Deferred Prosecution Agreement, United States v. The Boeing Company, No. 4:21-CR-005-O (N.D. Tex.); Ethiopian Aircraft Accident Investigation Bureau, Final Report No. AI-01/19, ET302 B737-8 MAX ET-AVJ accident of 10 March 2019 | high |
| Actor | MCAS, acting through the horizontal stabilizer trim | fact | Komite Nasional Keselamatan Transportasi (KNKT), Aircraft Accident Investigation Report, PT. Lion Mentari Airlines Boeing 737-8 (MAX) PK-LQP, Tanjung Karawang, West Java, 29 October 2018 | high |
| Inputs | A single angle-of-attack sensor; on both flights the sensor delivered erroneous data | fact | Komite Nasional Keselamatan Transportasi (KNKT), Aircraft Accident Investigation Report, PT. Lion Mentari Airlines Boeing 737-8 (MAX) PK-LQP, Tanjung Karawang, West Java, 29 October 2018; Ethiopian Aircraft Accident Investigation Bureau, Final Report No. AI-01/19, ET302 B737-8 MAX ET-AVJ accident of 10 March 2019 | high |
| Decision | Repeated activation, commanding nose-down trim each time the erroneous input persisted | fact | Ethiopian Aircraft Accident Investigation Bureau, Final Report No. AI-01/19, ET302 B737-8 MAX ET-AVJ accident of 10 March 2019 | high |
| Envelope: authority | Design authority was increased during development to a larger stabilizer movement than originally assessed (from a maximum of 0.6 to 2.5 degrees of stabilizer movement, in March 2016); activation did not require both sensors to agree | fact | House Committee on Transportation and Infrastructure (majority staff), Final Committee Report: The Design, Development and Certification of the Boeing 737 MAX | high |
| Envelope: basis | Boeing did not reevaluate its single- and multiple-failure assessments of MCAS after the 2016 design changes, as Boeing acknowledged in a December 2018 briefing to the FAA, according to the House committee report | assertion | House Committee on Transportation and Infrastructure (majority staff), Final Committee Report: The Design, Development and Certification of the Boeing 737 MAX | medium |
| Action | Repeated nose-down trim inputs the crews could not sustainably counter | fact | Ethiopian Aircraft Accident Investigation Bureau, Final Report No. AI-01/19, ET302 B737-8 MAX ET-AVJ accident of 10 March 2019 | high |
| Outcome | State: harm. 346 fatalities across two flights (189 on Lion Air 610, 157 on Ethiopian 302). Grounded worldwide from March 2019; in the United States from 13 March 2019 until the FAA rescinded its order on 18 November 2020, conditional on the required fixes; other regulators lifted their groundings later (the European Union Aviation Safety Agency on 27 January 2021). As of June 2026. | fact | Ethiopian Aircraft Accident Investigation Bureau, Final Report No. AI-01/19, ET302 B737-8 MAX ET-AVJ accident of 10 March 2019; Komite Nasional Keselamatan Transportasi (KNKT), Aircraft Accident Investigation Report, PT. Lion Mentari Airlines Boeing 737-8 (MAX) PK-LQP, Tanjung Karawang, West Java, 29 October 2018; FAA, Rescission of the 737 MAX emergency order of prohibition (return to service), 18 November 2020; EASA declares Boeing 737 MAX safe to return to service in Europe | high |
| Evidence: pre-action warning | On the Lion Air flight the day before the crash the same behavior occurred; after an off-duty pilot in the jump seat noted the aircraft was diving, the Captain cut out the stabilizer trim and the crew continued on manual trim; the aircraft flew again | fact | Komite Nasional Keselamatan Transportasi (KNKT), Aircraft Accident Investigation Report, PT. Lion Mentari Airlines Boeing 737-8 (MAX) PK-LQP, Tanjung Karawang, West Java, 29 October 2018 | high |
| Evidence: causality | Both investigations identify MCAS activation on erroneous sensor data as central; the House report adds design, certification and disclosure failures. The US National Transportation Safety Board, which took part in the Ethiopian investigation, agrees on the role of MCAS but disputes parts of the Ethiopian report: it says the report gave crew performance insufficient attention; where the Ethiopian report attributes the sensor malfunction to a production-related electrical failure, the Board found the sensor vane was separated by a foreign object, most likely a bird; and it calls the finding on missing MCAS documentation for crews misleading, because Boeing had given the information to all 737 MAX operators four months before the crash | assertion | House Committee on Transportation and Infrastructure (majority staff), Final Committee Report: The Design, Development and Certification of the Boeing 737 MAX; Komite Nasional Keselamatan Transportasi (KNKT), Aircraft Accident Investigation Report, PT. Lion Mentari Airlines Boeing 737-8 (MAX) PK-LQP, Tanjung Karawang, West Java, 29 October 2018; Ethiopian Aircraft Accident Investigation Bureau, Final Report No. AI-01/19, ET302 B737-8 MAX ET-AVJ accident of 10 March 2019; NTSB Publishes Additional Comments on Ethiopia's Final Report on 737 MAX 8 Accident | high |
| Recovery: automated fallback | None; the system did not recognize its own input as erroneous | interpretation | Komite Nasional Keselamatan Transportasi (KNKT), Aircraft Accident Investigation Report, PT. Lion Mentari Airlines Boeing 737-8 (MAX) PK-LQP, Tanjung Karawang, West Java, 29 October 2018 | high |
| Recovery: technical | The Ethiopian report records that on ET302 the crew cut out the stabilizer trim after the second MCAS activation; with electric trim off, the first officer said the trim was not working, tried it manually and said 'It is not working' at about 340 knots, and the two pilots held 80 to 110 lb on the control column, the nose rising only when both pulled. About two and a half minutes later the crew returned the cutout switches to normal; about five seconds after their next electric trim input a fourth activation moved the stabilizer from 2.3 to 1 unit, and the nose kept dropping despite up to 180 lb of column force | assertion | Ethiopian Aircraft Accident Investigation Bureau, Final Report No. AI-01/19, ET302 B737-8 MAX ET-AVJ accident of 10 March 2019 | medium |
| Recovery: accountability | Deferred prosecution agreement with the Department of Justice, January 2021, on a charge of conspiracy to defraud the United States over MCAS: $243.6 million criminal penalty, $1.77 billion to airline customers, and a $500 million fund for the families of those killed (about $2.5 billion in total). On 14 May 2024 the Department told the court it had determined that Boeing breached the agreement by failing to design, implement and enforce a compliance and ethics program. On 5 December 2024 the court rejected a plea agreement the parties had submitted in July 2024. Under a non-prosecution agreement of 29 May 2025, Boeing admitted the facts amounted to conspiracy to defraud the United States by obstructing the FAA's Aircraft Evaluation Group, and agreed to pay a further $243.6 million penalty, $444.5 million for the victims' families and at least $455 million for compliance and safety programs. On 6 November 2025 the court dismissed the charge at the Department's request, while writing that the agreement 'fails to secure the necessary accountability to ensure the safety of the flying public'; the federal appeals court denied the families' petitions against the agreement and the dismissal (revised opinion, 22 May 2026). Civil suits by the families are not recorded here | fact | Deferred Prosecution Agreement, United States v. The Boeing Company, No. 4:21-CR-005-O (N.D. Tex.); Department of Justice letter to Judge Reed O'Connor on Boeing's breach of the deferred prosecution agreement, United States v. The Boeing Company, No. 4:21-cr-00005-O (N.D. Tex.), ECF No. 199; Non-Prosecution Agreement, United States v. The Boeing Company, No. 4:21-cr-00005-O (N.D. Tex.), 29 May 2025; Memorandum Opinion and Order granting the Government's motion to dismiss the Information, United States v. The Boeing Company, No. 4:21-cr-5-O (N.D. Tex.), ECF No. 358; In re Naoise Connolly Ryan, et al., Nos. 25-11253 and 25-11254 (5th Cir.), revised opinion on petitions for rehearing, 22 May 2026 | high |
Controls
| Status | Control | Canonical |
|---|---|---|
| failed | Authority limits | C-E6 Authority limit on automation over humans |
| failed | Disclosure to operators | C-M1 Mandate disclosed to supervisor |
| failed | Single-sensor dependence; Sensor disagreement check gating activation (absent) | C-I2 Input redundancy and disagreement check |
| failed | Certification of MCAS (the House committee report identifies certification failures) | C-O2 Independent assurance before deployment |
| failed | Crew recovery on the Lion Air flight the day before: after a jump-seat pilot noted the dive, the Captain cut out the stabilizer trim (one occurrence). On Ethiopian 302 the crew also cut out the trim, could not trim manually, and returned the switches to normal about two and a half minutes later, before the fourth activation | C-R3 Human takeover with a time window |
| absent | No limit on repeated activations: MCAS commanded another nose-down input whenever the high reading persisted five seconds after a pilot trim input; each input was limited to 2.5 degrees of stabilizer movement | C-X1 Rate and magnitude limits |
Unmapped
- Assurance before action: the safety assessment that should have reflected the final design did not
- Pre-action warning available to the principal: the prior flight's recovery
Inference
inference Before the Lion Air crash, the pilots supervising the Maneuvering Characteristics Augmentation System (MCAS), an automatic nose-down trim function, had not been told it existed: the manufacturer, with the approval of the Federal Aviation Administration, removed it from the flight crew manual and training materials, and the Indonesian investigators found the missing guidance made it harder for crews to respond. That is not the whole record. The Lion Air crew the day before recovered without knowing of MCAS by cutting out the stabilizer trim, and the Ethiopian crew had received the bulletin and emergency directive issued after the first crash, which pointed to the cutout switches; the Ethiopian investigators say that guidance did not have its intended effect. Both investigations also list the single sensor, the repeated activations and the many alerts the crews faced at once. The record does not settle how much turned on disclosure: a federal court found in October 2022, in ruling that the families could assert rights as representatives of crime victims, that had Boeing not concealed MCAS's expansion to low speeds from the Federal Aviation Administration group that set pilot training requirements, neither crash would have occurred, while the United States National Transportation Safety Board calls the Ethiopian finding on missing MCAS documentation misleading. The agent-world equivalent is an operator who has not been told what the agent is allowed to do.
Sources
| ID | Record | Type | Link |
|---|---|---|---|
| DOJ-BA | Deferred Prosecution Agreement, United States v. The Boeing Company, No. 4:21-CR-005-O (N.D. Tex.) | court primary record | justice.gov ↗ checked 2026-10-13 |
| ETH-AIB | Ethiopian Aircraft Accident Investigation Bureau, Final Report No. AI-01/19, ET302 B737-8 MAX ET-AVJ accident of 10 March 2019 | regulator primary record | bea.aero ↗ checked 2026-10-13 |
| HOUSE | House Committee on Transportation and Infrastructure (majority staff), Final Committee Report: The Design, Development and Certification of the Boeing 737 MAX | public record primary record | democrats-transportation.house.gov ↗ checked 2026-10-13 |
| KNKT | Komite Nasional Keselamatan Transportasi (KNKT), Aircraft Accident Investigation Report, PT. Lion Mentari Airlines Boeing 737-8 (MAX) PK-LQP, Tanjung Karawang, West Java, 29 October 2018 | regulator primary record | knkt.go.id ↗ checked 2026-10-13 |
| FAA-RTS | FAA, Rescission of the 737 MAX emergency order of prohibition (return to service), 18 November 2020 | regulator primary record | faa.gov ↗ checked 2026-10-13 |
| DOJ-BREACH | Department of Justice letter to Judge Reed O'Connor on Boeing's breach of the deferred prosecution agreement, United States v. The Boeing Company, No. 4:21-cr-00005-O (N.D. Tex.), ECF No. 199 | court primary record | static.maglaw.com ↗ checked 2026-10-20 |
| DOJ-NPA | Non-Prosecution Agreement, United States v. The Boeing Company, No. 4:21-cr-00005-O (N.D. Tex.), 29 May 2025 | court primary record | justice.gov ↗ checked 2026-10-20 |
| DISMISSAL | Memorandum Opinion and Order granting the Government's motion to dismiss the Information, United States v. The Boeing Company, No. 4:21-cr-5-O (N.D. Tex.), ECF No. 358 | court primary record | justice.gov ↗ checked 2026-10-20 |
| CA5-2026 | In re Naoise Connolly Ryan, et al., Nos. 25-11253 and 25-11254 (5th Cir.), revised opinion on petitions for rehearing, 22 May 2026 | court primary record | justice.gov ↗ checked 2026-10-20 |
| EASA-RTS | EASA declares Boeing 737 MAX safe to return to service in Europe | regulator primary record | easa.europa.eu ↗ checked 2026-10-20 |
| NTSB-ET302 | NTSB Publishes Additional Comments on Ethiopia's Final Report on 737 MAX 8 Accident (interest: accredited representative of the state where the aircraft was designed and built) | regulator primary record | ntsb.gov ↗ checked 2026-10-20 |
| CVRA-2022 | Second Memorandum Opinion and Order (Crime Victims' Rights Act), United States v. The Boeing Company, No. 4:21-cr-5-O (N.D. Tex.), 21 October 2022, ECF No. 116 | court primary record | justice.gov ↗ checked 2026-10-21 |