MCAS
Definition
Maneuvering Characteristics Augmentation System; the Boeing 737 MAX software feature that repeatedly commanded nose-down stabiliser trim based on a single AoA sensor input, causing two fatal crashes in 2018-2019.
- Full name
- Maneuvering Characteristics Augmentation System
- Aircraft
- Boeing 737 MAX
- Failure mode
- Repeated nose-down trim from a single AoA sensor
- Outcome
- Two fatal crashes, 2018 to 2019
Common questions
Why is a single sensor input treated as a critical design flaw?+
MCAS relied on one angle-of-attack sensor without cross-checking a second sensor or requiring pilot confirmation before repeatedly commanding trim, so a single faulty sensor reading could trigger a runaway control input with no built-in redundancy check.
Why does this case appear in forensic engineering / failure analysis material?+
It illustrates how a software control-system design decision, not a material or structural fracture, can be the proximate cause of catastrophic failure, broadening failure analysis beyond purely mechanical fractography.
Related terms
- Beach Marks
- Macroscopic curved bands on a fatigue fracture surface, visible without magnification, produced by changes in crack growth rate during service (load changes,...
- Damage-Tolerant Design
- A structural-design philosophy that assumes cracks will form and specifies inspection intervals short enough to detect and repair cracks before they reach...
- Ductile Dimples
- Microscopic cup-shaped depressions visible on a ductile overload fracture surface under SEM, formed by nucleation, growth, and coalescence of microvoids at second-phase...
- Fatigue Striations
- Microscopic parallel marks on a fatigue fracture surface, formed during individual loading cycles in Stage II crack growth. Visible by SEM at...
- Fractography
- The systematic examination and interpretation of fracture surfaces to determine the mechanism, origin, and propagation direction of fracture; uses optical and scanning...
- Progressive Collapse
- A failure mode in which local structural failure triggers a sequence of failures in adjacent members, resulting in collapse disproportionate to the...
- River Patterns
- Fan-shaped or river-delta-like markings on brittle-cleavage fracture surfaces that indicate crack propagation direction; rivers diverge from the origin and converge toward the...
- S-N Curve
- A plot of cyclic stress amplitude (S) against the number of cycles to failure (N), used to characterise a material's fatigue life;...
- Safe-Life Design
- A structural-design philosophy where a component is retired from service before its predicted fatigue life is consumed; does not require crack detection...
- Stress-Concentration Factor (Kt)
- A dimensionless multiplier representing the ratio of the actual maximum stress at a notch, hole, or corner to the nominal stress in...
- Stress-Corrosion Cracking (SCC)
- A failure mode combining sustained tensile stress with a specific corrosive environment, producing branching, often intergranular cracks that grow at stress intensities...