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
- Identify HLS control and power channels.
- Explain slat, droop-nose and flap movement.
- Describe POB, WTB, torque and asymmetry protection.
- Interpret half-speed and locked conditions.
1. System purpose
High-lift devices increase lift and manage drag for takeoff and landing. The A350 combines leading-edge droop nose and slats with trailing-edge flaps. Flap-lever position, flight phase and system logic determine the demanded 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?
2. SFCC architecture
Two Slat Flap Control Computers each contain slat and flap channels. One channel can retain control after loss of the other, usually with reduced movement speed because only one motor or power path remains. The computers compare position sources and monitor overspeed, asymmetry, runaway, jam and uncommanded movement.
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. Slats and droop nose
Each wing has an inboard droop-nose device and outboard slat sections driven through rotary actuators and tracks. The slat PCU combines an electric and a hydraulic motor under separate SFCC control. Transmission brakes and wing-tip brakes can stop and lock the system after abnormal movement.
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. Flaps
The flap PCU uses redundant hydraulic drive and transmits power across the wings. Active differential gearing can alter outboard-flap movement for performance optimization. Position pickup units and torque monitoring allow the computers to detect disagreement and excessive torsional load.
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. Spoiler and flap coordination
Spoilers and flaps are not mechanically coupled, but PFCS commands spoiler droop to maintain the required gap and avoid clash. A spoiler that cannot reach the required position can inhibit flap retraction and generate an indication.
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 reasoning
A locked or slow system can result from control-channel loss, motor loss, brake engagement, transmission jam, position disagreement or torque detection. Confirm which SFCC channel and power path remain, compare commanded and actual position, and follow approved tests. Never manually release a protection device without the applicable maintenance procedure.
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
- Identify HLS control and power channels.
- Explain slat, droop-nose and flap movement.
- Describe POB, WTB, torque and asymmetry protection.
- Interpret half-speed and locked conditions.
Current approved maintenance data always controls aircraft work.
