Educational familiarization only. This is original TechOpsBase learning content created from privately supplied legacy training and MSG-3 source material. It does not reproduce manufacturer pages, proprietary diagrams, task steps, numerical maintenance limits, dispatch criteria or controlled maintenance data. Current approved aircraft data, effectivity and operator procedures govern all aircraft work.
Resource profile
- Aircraft: Airbus A350 family
- ATA chapter: 42 — Integrated Modular Avionics
- Resource: A350 ATA 42 CRDC Redundancy and Subscriber Impact
- Level: Intermediate-to-advanced
- Status: Draft pending technical review
Learning objectives
- Explain subscriber-specific redundancy.
- Differentiate redundant and single signals.
- Interpret one-CRDC loss.
- Use mapping in troubleshooting.
- Avoid false backup assumptions.
1. Purpose and operational value
CRDC redundancy is designed by signal and subscriber allocation rather than by a simple primary/backup box relationship.
2. Architecture and system flow
Most safety-relevant signals are connected to multiple CRDCs in parallel or through independent paths.
Some lower-criticality data can use one CRDC only.
The loss of a CRDC therefore affects a unique set of users and signals; maintenance must use the actual allocation table.
3. Major components and functions
Subscriber mapping
Defines which users use each CRDC/channel. The component must receive the correct input, perform its intended function and provide a valid output or status. A maintenance diagnosis must separate loss of power, loss of communication, incorrect configuration, blockage or leakage, contamination, mechanical degradation and an upstream or downstream interface failure. Useful evidence includes affected-function list and signal routing. Command, feedback and physical effect must agree before hardware is condemned.
Redundant signal paths
Provide alternate acquisition/output. The component must receive the correct input, perform its intended function and provide a valid output or status. A maintenance diagnosis must separate loss of power, loss of communication, incorrect configuration, blockage or leakage, contamination, mechanical degradation and an upstream or downstream interface failure. Useful evidence includes remaining path, comparison and degraded status. Command, feedback and physical effect must agree before hardware is condemned.
Single-occurrence signals
Have no CRDC redundancy. The component must receive the correct input, perform its intended function and provide a valid output or status. A maintenance diagnosis must separate loss of power, loss of communication, incorrect configuration, blockage or leakage, contamination, mechanical degradation and an upstream or downstream interface failure. Useful evidence includes specific loss and operational consequence. Command, feedback and physical effect must agree before hardware is condemned.
FWS/dispatch logic
Reports subscriber and common-resource effects. The component must receive the correct input, perform its intended function and provide a valid output or status. A maintenance diagnosis must separate loss of power, loss of communication, incorrect configuration, blockage or leakage, contamination, mechanical degradation and an upstream or downstream interface failure. Useful evidence includes message combination and root-cause indication. Command, feedback and physical effect must agree before hardware is condemned.
Configuration data
Defines user-to-CRDC relationships. The component must receive the correct input, perform its intended function and provide a valid output or status. A maintenance diagnosis must separate loss of power, loss of communication, incorrect configuration, blockage or leakage, contamination, mechanical degradation and an upstream or downstream interface failure. Useful evidence includes aircraft effectivity and installed software. Command, feedback and physical effect must agree before hardware is condemned.
4. Normal operating sequence
1. Normal
Multiple paths provide equivalent data where designed.
2. One CRDC lost
Subscribers continue through available paths or lose single signals.
3. Degraded mode
Warnings/dispatch identify remaining capability.
4. Repair
Correct module, power, wiring or configuration and verify every affected subscriber.
5. Control, monitoring and protection
The statement 'another CRDC is available' is incomplete without knowing whether the specific signal is redundant.
A CRDC replacement must restore all mapped subscribers, not only the first reported system.
6. Failure modes and maintenance reasoning
- Unexpected multiple-system impact: Shared CRDC allocation.
- Only one function lost: Single channel/signal or no redundancy.
- Disagreement between paths: Sensor/wiring/channel or conversion issue.
- Replacement partially restores: Additional channel, wiring or configuration issue.
- No alert for lost low-criticality signal: Evidency/monitoring design may differ.
7. Interfaces with other aircraft systems
- Hosted applications in CPIOMs.
- AFDX network.
- Remote aircraft-system equipment.
- FWS/CMS.
- Configuration/loading.
8. Practical maintenance scenarios
One CRDC loss leaves most functions normal
Check the specific single-occurrence users.
Two systems disagree on same sensor
Trace which CRDC path each receives.
After replacement one subscriber remains absent
Verify its physical channel and allocation.
9. Technician takeaways
- Redundancy is signal-specific.
- Use subscriber maps.
- Verify all impacted users.
- Configuration is part of the redundancy design.
Maintenance boundary
This resource explains architecture, operation, indications and system-level troubleshooting. It intentionally excludes removal/installation instructions, wiring-pin checks, maintenance limits, software part numbers, servicing quantities, inspection intervals and release-to-service criteria.
Review prompts
- What is the required system function?
- Which component commands, processes or physically performs it?
- Which power, fluid, pneumatic or data path is required?
- What command proves the function was requested?
- What feedback or physical effect proves correct operation?
- Which adjacent ATA system can create the same symptom?
- What evidence should be preserved before reset, draining, servicing or software action?
- What hygiene, electrical, pressure, network or safety boundary applies?
