Educational familiarization only. This original TechOpsBase resource explains system purpose, architecture and maintenance reasoning. It does not reproduce Airbus pages, diagrams, task instructions or controlled maintenance data. Actual aircraft work requires current approved data, correct effectivity, operator procedures, authorization and supervision.
Resource profile
- Aircraft: Airbus A350 family
- ATA chapter: 27 - Flight Controls
- Audience: Students, junior technicians and working professionals
- Level: Intermediate familiarization
- Source basis: Privately supplied 2013-2014 manufacturer training and MSG-3 material
- Technical status: Draft pending technical review
Learning objectives
- Describe the purpose of each law family.
- Explain pitch and lateral-law objectives.
- Recognize protection loss as a system reconfiguration.
- Avoid treating law status as a component diagnosis.
1. Why control laws exist
A fly-by-wire aircraft does not send pilot-stick displacement directly to a control surface in normal operation. Computers interpret the command together with aircraft state. The result is predictable handling, damping, coordination, load management and—when available—envelope protection. The law is therefore a software-defined relationship between pilot intent, sensed condition and surface response.
Maintenance questions to ask
- What is the commanded condition and what independent evidence confirms it?
- Which computer, sensor, hydraulic and electrical channels are required in this configuration?
- Is the failure crew-evident, maintenance-evident or hidden until a dedicated test?
- Which current approved document and effectivity control the next action?
2. Normal law
Normal law provides the intended handling qualities. Pitch functions can control load factor, pitch rate and angle of attack while lateral functions coordinate roll and yaw. Protections can limit angle of attack, excessive speed, load factor or bank behavior. Automatic trim reduces steady pilot force. These capabilities depend on valid air, inertial, configuration and surface data.
Maintenance questions to ask
- What is the commanded condition and what independent evidence confirms it?
- Which computer, sensor, hydraulic and electrical channels are required in this configuration?
- Is the failure crew-evident, maintenance-evident or hidden until a dedicated test?
- Which current approved document and effectivity control the next action?
3. Alternate and abnormal laws
When required data or redundancy is lost, the computers may retain controlled response but remove or alter one or more protections. Alternate law is not one fixed condition; its available features depend on the failures that caused reconfiguration. Abnormal law addresses specific data conditions that make normal objectives inappropriate. Maintenance interpretation must start from the triggering faults and available sources.
Maintenance questions to ask
- What is the commanded condition and what independent evidence confirms it?
- Which computer, sensor, hydraulic and electrical channels are required in this configuration?
- Is the failure crew-evident, maintenance-evident or hidden until a dedicated test?
- Which current approved document and effectivity control the next action?
4. Direct law
In direct law the relationship between stick input and surface command becomes more direct. Stabilizing feedback can remain to provide adequate damping, but automatic trim or protections can be reduced. The THS may need manual control. Direct law is a valid designed configuration, not proof of an actuator fault.
Maintenance questions to ask
- What is the commanded condition and what independent evidence confirms it?
- Which computer, sensor, hydraulic and electrical channels are required in this configuration?
- Is the failure crew-evident, maintenance-evident or hidden until a dedicated test?
- Which current approved document and effectivity control the next action?
5. Protections
Angle-of-attack protection introduces low-speed stability and limits stall approach. High-speed protection limits speed or Mach excursions. Load-factor and bank-angle functions shape pilot authority. Protection availability is shown to the crew and depends on sensor validity, computer capability and aircraft configuration.
Maintenance questions to ask
- What is the commanded condition and what independent evidence confirms it?
- Which computer, sensor, hydraulic and electrical channels are required in this configuration?
- Is the failure crew-evident, maintenance-evident or hidden until a dedicated test?
- Which current approved document and effectivity control the next action?
6. Maintenance interpretation
A law downgrade is an end result of system logic. Read the associated warnings and maintenance reports, identify lost inputs or computers, and confirm whether the surface-control channels remain available. Never infer that a named law directly identifies the replaceable unit.
Maintenance questions to ask
- What is the commanded condition and what independent evidence confirms it?
- Which computer, sensor, hydraulic and electrical channels are required in this configuration?
- Is the failure crew-evident, maintenance-evident or hidden until a dedicated test?
- Which current approved document and effectivity control the next action?
Integrated review
Use the input ? computation ? power ? actuation ? feedback ? indication model. A correct diagnosis must explain both the physical symptom and every associated message. Avoid replacing a computer merely because it generated the warning; it may be reporting loss of an external input, power source or actuator response.
Key takeaways
- Describe the purpose of each law family.
- Explain pitch and lateral-law objectives.
- Recognize protection loss as a system reconfiguration.
- Avoid treating law status as a component diagnosis.
Current approved maintenance data always controls aircraft work.
