Redundancy in AGL Electrical Architecture Dual Circuits, Backup Power & Fault-Tolerant Airport Lighting
See how dual runway circuits, independent feeders, CCRs, UPS and DG backup, ALCMS and fail-safe control combine so that one failure does not take away the visual guidance a runway needs, and why two of everything is not the same as redundancy.
What Is Redundancy in AGL Electrical Architecture?
Redundancy in Airfield Ground Lighting (AGL) means designing the electrical and control system so that a single equipment or circuit failure does not unnecessarily remove the required airport visual guidance. It matters most for precision approach runways, CAT II/III operations, low-visibility procedures, runway centreline, edge and touchdown-zone lighting, stop bars, critical approach lighting and essential taxiway lighting.
A redundant AGL system is not simply a system with “two of everything.” The engineering objective is to maintain the required lighting service after a defined single failure, with the required continuity and without creating misleading or conflicting indications.
Redundancy has to be considered across the whole chain
Single system
One failure leads to loss of service.
Redundant system
One failure leaves an alternate path that continues service.
Different failures need different strategies
Interleaved Circuits: What Survives When a Circuit Fails?
Interleaving puts neighbouring lights on different circuits, so one circuit failure leaves a distributed pattern instead of a long dark section. Try the four cases.
How two interleaved series circuits share one row of lights.
AGL Visual Encyclopedia: Interleaved Series Circuits Alternate-Circuit Centreline Arrangement AGL Circuit Zones
The Layers of AGL Redundancy
Source redundancy
More than one power source.
Distribution redundancy
More than one independent feeder or bus.
CCR redundancy
Multiple regulators serving independent or appropriately distributed circuits.
Circuit redundancy
Two or more AGL circuits serve a lighting system.
Spatial redundancy
Lights are distributed between circuits instead of grouping adjacent lights on one circuit.
Equipment redundancy
Critical control or monitoring equipment has standby units.
Control redundancy
Failure of a processor or network component does not necessarily mean total loss of control.
Monitoring redundancy
Faults stay detectable even when part of the monitoring architecture fails.
A five-layer way to explain it
Redundancy is a stack of independent layers, not one duplicated box.
AGL Visual Encyclopedia: Single Point of Failure Analysis Serviceability of Critical Lights
Electrical vs Operational Redundancy, Single Points of Failure and Common Cause
Electrical redundancy
An alternate electrical path exists.
Operational redundancy
The airport can continue the required operation after the defined failure. Two CCRs do not guarantee this: the alternate CCR may be connected to the wrong part of the circuit, or a common cable section may still be a single point of failure.
The right design question is: what lighting function remains available after the defined failure?
Potential AGL single points of failure
Common-cause failures that defeat apparent redundancy
| Example | Why it defeats redundancy |
|---|---|
| One flood affects both circuits | Both circuits share the same exposure |
| One chamber fire damages both cables | Physical proximity |
| One switchboard feeds both CCRs | Shared electrical source |
| One network switch controls both systems | Shared control path |
| One software server controls everything | Shared logic |
| One grounding failure affects both circuits | Shared reference and protection path |
Redundant vs fail-safe
Redundant means a backup exists. Fail-safe means that when something fails, the system moves to or stays in a state that minimizes safety risk. Two controllers sending conflicting commands are redundant but not necessarily safe.
Redundancy vs resilience
Redundancy is an alternate path or capacity. Resilience is the airport’s wider ability to withstand and recover from disruption: redundancy plus protection, monitoring, maintenance, procedures, spares and recovery.
Ask of every link in the chain: what if it fails alone?
AGL Visual Encyclopedia: Single Point of Failure Analysis Dual Feeders and Incoming Supply Redundancy
A Redundant AGL Electrical Architecture
Representative layered arrangement. The actual topology depends on runway category, AGL configuration, operational requirements and the approved design.
Dual-Circuit Redundancy by Lighting System
| Lighting system | What redundancy is aiming for | Design considerations |
|---|---|---|
| Runway edge | Continuity after one circuit failure and distributed light availability | Circuit independence, physical separation, light distribution, transformer allocation |
| Runway centreline | Service maintained on the second circuit if one fails, especially on precision runways | Circuit design and remaining light serviceability |
| Runway end | Avoid losing the whole function on one circuit | Hidden common points of failure, maintenance, failure isolation |
| Threshold | A single circuit failure does not remove the complete threshold function | Distribution between circuits, checked against visual-aid and operational requirements |
| Touchdown zone | Support low-visibility operations | Fixture spacing, independent power, CCR allocation, fault detection, access |
| Approach | Maintain required visual guidance after defined failures | Which portions need secondary power. It is not necessarily right to duplicate every circuit |
| Taxiway | Limit a failure to a small area | Separate segments for edge, centreline, stop-bar and guard-light circuits |
| Stop bars | Defined, controlled state on failure | Supply, control, monitoring, switching, interlocking and field lighting together |
Independent vs dependent interleaved circuits
Independent interleaved
Each circuit has an electrical path sufficiently separated from the other, as set by the design. Stronger redundancy.
Dependent interleaved
Lights are interleaved physically but the circuits share some infrastructure or dependency. The consequence of losing one circuit differs.
Related Guides
Runway lighting systems Taxiway lighting systems Approach lighting systems Runway guard lights and stop barsAlternate circuits on a centreline, and what remains after one circuit is lost.
AGL Visual Encyclopedia: Alternate-Circuit Centreline Arrangement Interleaved Series Circuits Taxiway Circuit Arrangement
Source, UPS, DG and Switch-Over
| Arrangement | What it gives |
|---|---|
| Dual utility feed | Two independent utility feeders |
| Utility + DG | Grid plus standby generator |
| Utility + UPS + DG | UPS gives fast continuity, DG gives sustained backup |
| Dual DG | Two standby generators |
| Dual UPS | Two UPS systems serving critical loads |
| Independent substations | Separate infrastructure for different critical systems |
N+1
Capacity for the load plus one extra unit. If three modules are needed, install four. A shared input panel, output panel or battery can still be a single point of failure.
Parallel redundant
Units share load, and one can fail without losing the protected function.
2N
Two complete independent systems, each able to carry the critical load. Stronger and more expensive.
Redundancy is not the same as switch-over time
Redundancy
Can the system continue after a component failure?
Switch-over time
How quickly is service restored after the source fails? Two generators can still have an unacceptable transfer time, while an online UPS gives very fast continuity with a single generator behind it.
Generator sizing
Do not size from average AGL load. Use the critical-load schedule: which CCRs run together, starting currents, UPS charging, other essential loads, generator failure scenarios, expansion and load shedding.
UPS sizing
Reflect actual AGL load, control load, ALCMS, A-SMGCS interfaces, autonomy, battery ageing, growth and the chosen redundancy philosophy, assessed as a complete system.
Airport Lighting Power Calculation
An airport lighting power calculation starts from the critical-load schedule, not the average AGL load. Add up the loads that run together: the CCRs for each lighting circuit, control and ALCMS load, A-SMGCS interfaces and other essential loads. Then allow for CCR starting currents, UPS charging, expansion and load shedding. The same schedule feeds generator sizing, UPS sizing and the N+1 or 2N decision, so the result should be checked against each failure scenario rather than the normal case alone. For CCR and circuit-level loading, see the AGL Toolkit
Related Guides
Emergency backup power Emergency power and lighting systems ICAO aerodrome lighting requirementsTwo incoming feeders, a bus and what each fault leaves lit.
AGL Visual Encyclopedia: Dual Feeders and Incoming Supply Redundancy Standby power and UPS
Generator start, changeover and the gap the lights must ride through.
AGL Visual Encyclopedia: Generator changeover and switchover time Standby power and UPS
CCRs, Cable Routes, Transformers and Surge Protection
CCR redundancy
Two CCRs on two circuits give some redundancy, but two CCRs feeding one common cable still leave a single point of failure. Link the CCR study to circuit and cable topology, and prefer an architecture where a CCR failure affects one circuit, not a whole visual-aid system.
CCR failure modes
Power-electronics fault, controller failure, input breaker failure, output fault, cooling failure, communication failure and internal protection trip.
Physical separation
Two circuits in one duct remain exposed to excavation damage, flooding and fire. Plan route separation where feasible and review crossings, duct capacity, drainage, chambers, access and construction exposure.
Transformers and connectors
Individual isolation transformers mean a transformer failure normally removes one light, a natural form of distributed redundancy. Avoid one connector or chamber affecting several lights, and keep moisture ingress from propagating across circuits.
Redundant circuits must survive the same environment. Two circuits routed together and hit by one lightning or surge event may fail together, so coordinate redundancy with lightning protection, counterpoise, bonding, surge protection and cable routing.
Related Guides
Lightning and surge protection for AGL circuits Surge protection and lightning mitigation Airport isolating transformer Junction boxes and housingsA duty CCR, a standby CCR and the changeover between them.
AGL Visual Encyclopedia: Standby CCR and Changeover Arrangement CCR contactors and bypass CCR Failure Modes
Where surge protection sits on the CCR input, output and circuit.
AGL Visual Encyclopedia: Surge Protection Devices for CCR and Circuits Lightning/Surge Interface
ALCMS, Network, Field Controllers, A-SMGCS and Follow the Greens
ALCMS and network
A robust design may use a primary and standby server, two networks and two field controllers where the operational requirement justifies it. Separate lighting power from the control application so a server failure has a defined response. Field equipment may hold its last state, move to a default state or allow local or manual control. Test whichever is specified.
Field controllers
Controllers may drive CCRs, taxiway segments, stop bars, signs and Follow the Greens functions. A controller failure should give a defined safe response and an alarm.
Where AGL is integrated with A-SMGCS, the chain gets longer
For a safety-related lighting system the question is: what should the pilot see when the system is degraded? The answer should be unambiguous. Redundancy needs interlocking, monitoring and fail-safe logic with it.
Dual network paths between the ALCMS and field controllers.
AGL Visual Encyclopedia: Network Redundancy ALCMS Failure Flow ALCMS Communication Architecture
Redundancy Matrix and FMEA
Redundancy matrix: define the response to every failure
| Component | Failure | Desired response |
|---|---|---|
| Utility feeder | Utility loss | Transfer to secondary source |
| UPS | UPS failure | DG or alternate supply, or a defined degraded mode |
| DG | Generator failure | Alternate DG or utility where required |
| CCR | CCR failure | Alternate circuit or CCR |
| Runway circuit | Cable or circuit failure | Alternate circuit maintains required lighting |
| Transformer | Transformer failure | Affected light only |
| ALCMS server | Server failure | Standby server |
| Network | Link failure | Redundant communication path |
| Field controller | Controller failure | Backup controller or safe degraded mode |
| Stop bar | Control failure | Defined safe response |
| A-SMGCS interface | Data failure | Degraded or fallback operating procedure |
Simplified FMEA
| Failure | Local effect | System effect | Mitigation |
|---|---|---|---|
| CCR-A failure | Circuit A lost | Partial runway lighting | CCR-B / circuit redundancy |
| Cable-A failure | Circuit A lost | Partial lighting | Interleaved Circuit B |
| Transformer failure | One light lost | Local | Remaining lights |
| Utility failure | Normal source lost | Potential full outage | UPS / DG |
| UPS failure | Fast backup lost | Changeover degradation | Secondary source |
| DG failure | Extended backup lost | Limited endurance | Alternate source |
| ALCMS server failure | Central control lost | Control degraded | Standby server / manual control |
| Network link failure | Communication lost | Partial control loss | Redundant network |
| Stop-bar controller failure | Stop-bar command affected | Holding-point risk | Fail-safe logic / fallback |
| Light fitting failure | Individual light lost | Local serviceability loss | Distributed lighting |
Redundancy claims are only as good as the failure modes they were checked against.
AGL Visual Encyclopedia: CCR Failure Modes Transformer Failure Modes Sign Failure Modes
CAT II/III, Serviceability and Maintenance
Low-visibility operations
Redundancy becomes an active operational condition. LVP readiness can depend on circuit redundancy, power redundancy, equipment serviceability and control availability together. AAI’s airport procedures link specific circuit and light failures to restrictions on CAT II/III operations; those limits are airport-specific.
Redundancy vs serviceability
Redundancy gives resilience. Serviceability criteria define how much degradation is acceptable. A failed Circuit A does not mean everything is acceptable indefinitely: Circuit B still has to meet the applicable limits.
Maintenance configurations to define
| State | Meaning | Define |
|---|---|---|
| Normal | Both systems available | Baseline alarm status |
| Maintenance | One system intentionally unavailable | Restrictions, restoration procedure, communication |
| Degraded | One system failed unexpectedly | Alarm, operational restrictions, recovery |
| Emergency | Multiple failures | Procedures and escalation |
From serviceability measurement to a maintenance action.
AGL Visual Encyclopedia: Serviceability-Triggered Maintenance Flow Minimum Serviceable Lamp Percentages by Light Type Serviceability of Critical Lights
Proving Redundancy: Failure Simulation, Functional and Photometric Tests
Normal condition
Both redundant paths operational.
Circuit A failure
Disable Circuit A. Verify Circuit B stays available, the right lights stay lit, alarms appear and required operation is supported.
Circuit B failure
Repeat in the opposite direction.
Utility failure
Verify secondary power transfer and actual AGL restoration.
UPS and DG failure
Verify the defined backup source, alternate source or degraded mode.
CCR failure
Verify alternate circuit behaviour.
ALCMS and communication failure
Verify standby, local or manual control and the safe field state.
Photometry after failure
Verify the remaining lighting still meets the required optical performance.
Commissioning test matrix
| Test | Failure introduced | Expected result |
|---|---|---|
| Circuit A trip | Circuit A unavailable | Circuit B maintains required lighting |
| Circuit B trip | Circuit B unavailable | Circuit A maintains required lighting |
| Utility loss | Normal source unavailable | Secondary source takes over |
| UPS failure | UPS unavailable | Defined backup or degraded mode |
| DG-1 failure | Generator unavailable | Alternate source or approved restriction |
| CCR-A failure | CCR unavailable | Alternate circuit remains functional |
| ALCMS server failure | Primary server unavailable | Standby or control fallback operates |
| Network link failure | One communication path lost | Redundant path remains available |
| Field controller failure | Controller unavailable | Defined safe state |
| Stop-bar control failure | Command path unavailable | Safe operational response |
| Photometry | Post-failure measurement | Required optical performance verified |
A redundant design is only proven when the failure has actually been simulated.
AGL Visual Encyclopedia: Generator changeover and switchover time Cable Testing (Commissioning) Commissioning Sequence
From Requirement to Redundancy Philosophy
Define the operational requirement
Runway category and required visual aids.
Identify critical loads
Which systems need continuity.
Map the existing architecture
Power, CCRs, circuits and controls.
Identify single points of failure
Where one fault causes unacceptable loss.
Develop the redundancy philosophy
Source, circuit and control redundancy.
Check physical independence
Cable routes, switchgear and common systems.
Design protection
Lightning, surge and grounding.
Design control
Fail-safe switching and monitoring.
Develop the failure matrix
Response to each defined failure.
Test
Electrical, functional, redundancy and photometric tests.
Document
Drawings, cause and effect, test results.
Maintain
Periodically prove redundancy is still available.
The sequence is Requirement → Failure Analysis → Redundancy Philosophy → Design, not “install two of everything.” Not every airport needs 2N UPS, N+1 DG, dual independent feeders or two CCRs for every lighting system.
Example gap assessment (illustrative values)
| Category | Existing | Required | Gap |
|---|---|---|---|
| Utility | Single | Dual / independent | High |
| UPS | Single | N+1 | Medium |
| Runway edge | Dual interleaved | Independent | Low |
| Cable route | Common | Separated | High |
| ALCMS | Single | Redundant | High |
| Stop bar | Single controller | Fail-safe | Medium |
| Photometry | Periodic | Failure verification | Medium |
Documents a redundancy project should deliver
AGL Power Supply System & Airfield Lighting Circuit Protection
How the lighting is fed and how the circuits are protected.
AGL power supply system
An AGL power supply system takes power from the airport's electrical supply to the CCRs, which feed the lighting series circuits. Redundancy is added through independent feeders, backup power such as UPS or a generator, and alternate circuits, according to the category of operation. The supply design should be checked against the standard the aerodrome follows.
Airfield lighting circuit protection
Airfield lighting circuit protection guards people and equipment against faults. It includes CCR protection such as open-circuit and overcurrent protection, earth fault monitoring, and upstream breakers and fuses. Settings come from the manufacturer's data and the project design, so none are given here. Good protection also helps locate faults quickly.
AGL Circuit Fault Troubleshooting: Open Circuit & Short Circuit Faults
Finding and understanding the two most common series-circuit fault types.
AGL circuit fault troubleshooting
AGL circuit fault troubleshooting starts with the symptom and the CCR status: tripped, low current, or high current. Make the circuit safe, then split it into sections and test each with insulation and loop resistance checks until the faulty section is found. Repair, re-test and record the cause. See the testing and failure simulation sections of this guide.
AGL open circuit fault
An AGL open circuit fault is a break in the series loop, such as a damaged cable, a failed joint or a poorly mated connector. Current stops flowing, and the CCR normally trips on its open-circuit protection. Never work on a series circuit that is open but energised. Locate the break by sectionalising the loop and checking continuity.
AGL short circuit fault
An AGL short circuit fault is an unwanted path in the circuit, often a short to earth caused by water or insulation damage. It can cause overcurrent, earth-fault alarms or a CCR trip. Locate the fault by sectionalising and insulation testing, then repair or replace the damaged cable, joint or transformer.
What an open circuit does to a series circuit.
AGL Visual Encyclopedia: Open Circuit Series Circuit Fault Path Cable Fault Location (TDR and Bridge Methods)
What a short circuit does to a series circuit.
AGL Visual Encyclopedia: Short Circuit Ground-Fault Detection and Insulation Monitoring Earth Fault
Redundancy Commissioning Checklist
Tick items as you go. Progress shows per group and is not saved.
Power
CCR and circuits
Field and control
Safety, optical and documents
Common Mistakes in AGL Redundancy Design
Two circuits, one common failure point
Two circuits in the same vulnerable cable route may fail together.
Two CCRs on one common supply
CCR duplication is ineffective if the common supply remains a single point of failure.
UPS without generator support
The UPS gives fast continuity but may not last a prolonged outage.
Generator without fast transfer
Long-duration power that fails the required visual-aid switch-over time.
Redundant power, single control
The lighting is powered but cannot be operated correctly because control failed.
Redundant control, single field circuit
Control survives, but the physical lighting still goes dark.
No failure testing
A system that looks redundant on paper can fail in a real outage.
No common-cause analysis
Duplicate components can still depend on one cable, room, network or control power source.
Standards and Regulatory Context
Use these together. They are framework and guidance documents, not substitutes for the approved project design.
Aerodromes: the principal international framework, including secondary power and switch-over provisions. Check the current edition, amendments and corrigenda.
Aerodrome Design Manual, Electrical Systems: specialist guidance for aerodrome electrical engineering.
Indian requirements referenced in AAI publications in connection with AGL serviceability and power.
Airport-specific AGL, UPS, DG and low-visibility procedures, useful as practical examples.
AGL Redundancy Engineering Services
Redundancy audit
Existing power sources, CCRs, circuits, cable routes, transformers, ALCMS and controls.
Electrical architecture
Single-line diagrams, circuit architecture, CCR allocation and critical-load classification.
Dual circuit design
Independent circuits, interleaving, segregation and fault isolation.
UPS / DG architecture
UPS, DG, ATS, secondary power and critical AGL loads.
ALCMS redundancy
Servers, networks, field controllers and control interfaces.
A-SMGCS and Follow the Greens
Fail-safe design for green centreline lighting, stop bars and control interfaces.
Failure analysis
FMEA, redundancy matrix, cause and effect and single-point-of-failure assessment.
Testing and commissioning
Circuit, power, CCR and control failure testing, plus photometric verification.
Existing-airport upgrade
Retrofit planning that improves reliability without replacing healthy infrastructure.
Quick Knowledge Check
Q1. What does a redundant AGL design aim to do?
Q2. Why are runway lights interleaved between two circuits?
Q3. Two circuits are interleaved but run in one duct. What is the main concern?
Q4. How do UPS and DG differ in the typical arrangement?
Q5. What does N+1 mean?
Explore More AGL Engineering
How Airfield Lighting Works
The whole chain from power to optics.
Open How Airfield Lighting Works →Emergency Power & Lighting Systems
UPS, DG and transfer.
Open Emergency Power & Lighting Systems →Airport Isolating Transformer
Ratings, types and testing.
Open Airport Isolating Transformer →ICAO Aerodrome Lighting Requirements
The ICAO AGL framework.
Open ICAO Aerodrome Lighting Requirements →AGL Photometry India
In-field photometric testing for Indian airports.
Open AGL Photometry India →Airport Lighting Companies India
Company types across the Indian AGL market.
Open Airport Lighting Companies India →Design for the Failure You Need to Survive.
Audit, architecture, testing and commissioning for reliable airport lighting power and circuits.
Explore the AGL Engineering Knowledge Hub
Fundamentals
Standards & Compliance
Runway, Taxiway & Approach Lighting
Surface Movement & Safety
PAPI
Electrical Engineering & Power
Photometry & Testing
Maintenance, Inspection & Safety
Resources, Documentation & Careers
AGL Redundancy FAQ
Q1What is redundancy in AGL?
AGL redundancy is the use of alternate power, circuit, equipment or control paths so that a defined single failure does not unnecessarily remove the required airport lighting function.
Q2Why are two AGL circuits used?
Two circuits can distribute runway lights so that failure of one circuit does not remove the entire lighting system. Interleaving can preserve spatial continuity.
Q3What is an interleaved AGL circuit?
A circuit arrangement in which adjacent lights are distributed between separate circuits rather than placing all consecutive lights on one circuit.
Q4Are two interleaved circuits automatically independent?
No. The circuits may still share common feeders, cable routes, switchgear, chambers or control systems.
Q5What is the difference between independent and dependent circuits?
Independent circuits have sufficiently separate electrical infrastructure to reduce common-cause failure. Dependent circuits can share infrastructure or dependencies.
Q6What does N+1 mean?
N+1 means providing the capacity required for normal operation plus one additional unit, so that one unit can fail without removing the required capacity.
Q7What is 2N redundancy?
2N means two independent complete systems, each capable of supporting the defined critical load.
Q8Does redundancy mean all runway lights stay on after one circuit fails?
Not necessarily. The remaining serviceability is defined by the applicable operational and regulatory criteria, which differ by lighting system, runway category and airport.
Q9Why are runway lights interleaved?
Interleaving spreads lights from separate circuits across the runway so that one circuit failure does not create a large continuous dark section.
Q10Does redundancy apply to CCRs?
Yes. CCR allocation can be an important part of circuit redundancy, provided the alternate path is sufficiently independent.
Q11Does a UPS provide redundancy?
A UPS provides power continuity. It is not automatically redundant. Redundant UPS architecture may use N+1, parallel or dual-independent arrangements.
Q12Why is a diesel generator needed when there is a UPS?
The UPS can give rapid continuity, while a generator can supply the system through a much longer outage.
Q13Is dual utility power better than UPS and DG?
Not universally. Each architecture has different characteristics. The right solution depends on source independence, switch-over requirements, outage duration, reliability and project requirements.
Q14How is AGL redundancy tested?
Engineers simulate defined failures such as circuit trip, CCR failure, utility loss, UPS failure, generator failure and control or network failure, then verify the system response and remaining lighting performance.
Q15Is photometry required after redundancy testing?
Where optical performance forms part of acceptance or verification, photometry can show that the remaining lighting performs as required after a simulated failure.
Q16What is the difference between redundancy and switch-over time?
Redundancy is whether the system can continue after a component failure. Switch-over time is how quickly service is restored after the source fails. They are separate engineering parameters.
Q17How to measure AGL circuit current?
Measure the series circuit current at the CCR output, using the CCR's own display or a calibrated clamp meter or current instrument rated for the circuit. Never open a live series circuit to insert a meter. Take readings at each brightness step, compare them with the rated current for that step, and record them. Work should be done by qualified staff under your site's safety procedure.
Q18How to check an airport lighting circuit?
Start with the CCR status and any alarms on the monitoring system, then measure the circuit current at the brightness steps. With the circuit isolated, test insulation resistance and loop resistance, and inspect connectors, transformers and fixtures along the circuit. Compare results with the commissioning records and acceptance limits, and record the findings.
Q19How to restore an airfield lighting circuit?
Make the circuit safe and find the cause before re-energising, rather than resetting repeatedly into a fault. Isolate the faulty section, repair or replace the damaged cable, joint, connector or transformer, then test insulation and continuity. Re-energise at a low brightness step, check the current, and return the circuit to service in agreement with air traffic control. Where redundancy exists, switch to the alternate circuit first. Record the fault and the repair.
Engineering & Expert Notes
Redundancy Has to Be Proven, Not Assumed
VerificationDrawings can show duplicated paths that share a single point of failure in practice. Test failure scenarios to confirm that the airfield stays serviceable.
Look for Hidden Common Points
Single PointsShared cable routes, ducts, control power or a common network switch can defeat apparent redundancy. Trace each path to its source.
Switch-Over Behaviour Matters as Much as the Backup Source
PowerA standby source that starts correctly may still disturb CCRs or controls during transfer. Test the transfer sequence under realistic load.
Control Redundancy Needs Its Own Check
ControlDual servers or networks protect the operator view but only help if failover is tested and the local fallback is understood by staff.
Use a Failure Matrix to Make Reviews Concrete
FMEAList each element, how it can fail and what happens to the lights. The table exposes unexpected consequences before an actual outage does.
Re-Test After Any Modification
Change ControlExtensions and upgrades can quietly remove a redundancy feature. Repeat the relevant failure tests after changes to the architecture.
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