“Follow the Greens” Concept AGL System Explained: Green Taxiway Centreline Lighting, Control & Airport Operations
How selectable green taxiway centreline segments, red stop bars, lighting control and ATC procedure combine into a dynamic visual route for pilots, and what it takes to design, test and maintain one.
What Is the “Follow the Greens” Concept?
“Follow the Greens” is an advanced airport surface-movement guidance concept in which selectable green taxiway centreline light segments give pilots a visual indication of the cleared taxi route. Instead of relying only on a full set of continuously lit centreline lights plus verbal turn-by-turn instructions, the airport lighting control system illuminates the appropriate green segments along the assigned route.
The illuminated green path acts as a dynamic visual route across the taxiway network. It is a visual guidance aid tied to an approved operational procedure. It is not permission to taxi.
The concept in one chain
Route and clearance limit
Control system / ALCMS
Selected segments lit
Signs and lookout continue
Clearance limit / hold
A cleared route lit in green, with a red stop bar ahead.
AGL Visual Encyclopedia: Follow-the-greens operation Selective Switching of Taxiway Lights Stop Bar Control
Route Simulator: What the Pilot Sees
Move the aircraft along the route, switch the system state and toggle the stop bar to see how the guidance changes and what the pilot should do.
Illustrative taxiway network. Drag the slider to move the aircraft along the cleared route.
Why Was “Follow the Greens” Developed?
As airports grow and taxiway networks become more complex, ground movement is harder to manage with static signs, markings and verbal instructions alone. In low visibility or at night the number of cues becomes harder to interpret.
An aircraft may need to navigate
A dynamic green-light route adds a visual layer that says: “This is the route currently selected for you.” It is most valuable where the airport has an integrated surface-movement control system.
The Building Blocks of a Follow the Greens System
Green taxiway centreline lights
Provide the directional visual path.
Red stop bars
Control where an aircraft must stop and give a strong stop/hold indication.
Taxiway lighting control system
Decides which centreline segments are illuminated.
Ground surveillance / position data
In some implementations, aircraft position decides which segments are active.
ATC
The controller authorizes and manages the movement route.
Signs and markings
Remain part of the pilot’s positional awareness.
Simplified architecture
Clearance
Taxiway lighting control
Segment selection
Field lighting
Visual guidance
Switching taxiway centreline lights section by section.
AGL Visual Encyclopedia: Selective Switching of Taxiway Lights ALCMS-to-Taxiway Taxiway Centreline Configuration
How Follow the Greens Works
Aircraft requests or receives taxi clearance
The pilot communicates with ATC, and ATC establishes the intended route and clearance limit.
ATC selects the route
The controller or surface-movement control system selects the relevant taxi route.
Green centreline segments illuminate
The centreline lighting system activates the appropriate sections of green taxiway centreline lights.
Pilot follows the green path
The pilot uses the lights for direction while keeping watch on markings, signs, the clearance, stop bars, other traffic and ATC instructions.
Previously used segments are extinguished
As the aircraft progresses, some implementations switch off lighting behind it and light new sections ahead.
Stop bars control crossing points
At protected holding positions red stop bars can stay on until ATC authorizes the aircraft to proceed.
Phraseology and Why It Does Not Replace ATC
Phraseology
Where an airport has an approved procedure, “FOLLOW THE GREENS” becomes part of the taxi instruction, normally together with a clearance limit. Published procedures give worked examples of route instructions that include both.
Guidance vs clearance
The lights provide directional guidance. ATC provides operational clearance and control. The pilot stays responsible for the clearance, wingtip clearance and other hazards.
Dynamic lighting is guidance, not an autonomous replacement for operational control.
What Airports Have Published
| Airport | What the published material describes | Notes |
|---|---|---|
| Dubai International (OMDB) | Taxiing guidance using stop bars and selectable segments of green centreline lights. Position data from a ground-surveillance system controls roughly the next 300 m of selected green lighting. Guidance lights lead to runway holding positions, and red stop bars are normally on unless the tower controller deselects them. Guidance is for night and low visibility, and not only then. | The 300 m figure is an airport-specific detail. Based on the published OMDB AIP as cited in the source material; confirm against the current AIRAC edition. |
| Singapore Changi (WSSS) | AIP Supplement 117/2026, effective 6 August 2026, gives pilots dedicated visual guidance while taxiing at night and in low visibility. ATC uses the phraseology with a verbal clearance limit. Pilots do not taxi ahead if there are no green lights or a red stop bar is lit. If routes are ambiguous or several green segments are visible, pilots stop and seek confirmation. The procedure is not available on runways or rapid-exit taxiways. | Checked against the published supplement. It follows an earlier supplement (052/2026) effective 19 March 2026. |
| Indian aerodromes (e.g. Cochin, Hyderabad) | AAI eAIP entries show green centreline lighting already in use, such as inset bidirectional green centreline lights and unidirectional green lights on rapid-exit taxiways. Other entries show alternate-colour and CAT III centreline arrangements. | Green centreline lighting is not the same as a Follow the Greens procedure. Whether a given airport runs the full procedure needs separate confirmation in its AIP and operational documents. |
Follow the Greens vs Conventional Taxiway Lighting
| Conventional taxiway guidance | Follow the Greens |
|---|---|
| Static lighting arrangement | Dynamically selected lighting route |
| Pilot interprets the full taxiway network | Selected route is visually emphasized |
| Heavy reliance on signs, markings and verbal routing | ATC plus a dynamic green route |
| Centreline may stay continuously lit | Selected segments can be controlled |
| Limited route-specific indication | Route-specific visual indication |
| Less integrated | Closely integrated with surface movement control |
Green centreline lighting
A physical lighting characteristic.
Follow the Greens
An operational and control concept that uses selected green centreline lighting to give dynamic route guidance.
The two terms are not interchangeable. An airport can have green taxiway centreline lights without a Follow the Greens procedure.
The same taxiway, lit two ways.
AGL Visual Encyclopedia: Follow-the-greens operation Taxiway Centreline Lights
Green Guidance, Red Stop Bars and Interlocking
Green = follow the route
The selected green path shows where to go.
Red stop bar = stop
At protected runway entries or holding positions the stop bar is a stronger control indication than continuing along a green route. Pilots do not proceed past an illuminated red stop bar, or when there are no green lights ahead after being told to follow the greens. Exact rules come from the airport’s approved procedure.
Typical interlocking logic
Command accepted
Segments lit
Position known
Interlock
Controller action
As approved
A route command should never simply switch lights on without considering protected crossings. The exact interlocking logic must be developed and validated as part of the airport’s approved system design.
How stop bars are switched with the cleared route.
AGL Visual Encyclopedia: Stop Bar Control Stop Bar Lights Stop Bar Monitoring
Follow the Greens System Architecture
Representative architecture. An advanced system may add: aircraft position → surface surveillance → route control logic.
The field lighting is still ordinary AGL electrical infrastructure. Where a series circuit is used: CCR → primary AGL cable → isolating transformer → light. The control system chooses which segments or circuits are active, while the CCR keeps the electrical conditions the circuit needs. A Follow the Greens project therefore covers lighting, electrical, control, communication, surveillance and operational procedures, not software alone.
ALCMS, Surveillance, A-SMGCS and the Controller Interface
A conventional ALCMS monitors
- CCR status
- Lamp circuits
- Alarms
- Lighting switching
- Brightness
A Follow the Greens system may also manage
- Route objects and taxiway segments
- Route conflicts
- Stop-bar states
- Position-based activation and extinguishing
- Controller commands and route progress
- Event history
Ground surveillance
Aircraft position can feed route logic: aircraft position → route logic → lighting command → green segment selection. The lighting then responds to the aircraft’s progress rather than being only a static layer. Not every implementation needs this.
Place in A-SMGCS
Follow the Greens can be one layer of an A-SMGCS architecture: surveillance detects where traffic is, routing and control set the approved route, lighting shows it, and ATC monitors compliance. Automation varies widely between airports.
Controller HMI
Poor HMI design can undermine a capable system. The controller should quickly see: which route is active, which aircraft it belongs to, where the aircraft is, which stop bar is active and whether any part of the route is unavailable. Useful displays include the ground map, active aircraft, selected route, green-light and stop-bar status, clearance limit, and fault, communication and surveillance status.
How surface surveillance and lighting control work together.
AGL Visual Encyclopedia: SMGCS and A-SMGCS lighting Surface Movement Radar Vehicle Detection Sensor
Segmentation, Intersections, LED Fittings, Cabling and Civil Works
Network segmentation
The centreline network is divided into logical segments, for example Segment 01 → 02 → 03 → 04. Each segment ties to a location, circuit, light fittings, a control address, a route function and status monitoring. This builds a digital representation of the physical airfield.
Complex intersections
With conventional lighting several visual paths may appear at once. Dynamic route selection can light only the intended route. Route lighting must be designed so that conflicting routes are never displayed in a confusing way.
LED centreline fittings
LED fittings suit dynamic architectures because they can offer fast, controllable switching and monitoring features, depending on the equipment. Select on complete project requirements, not on the nominal LED technology.
Cabling and circuits
Dynamic routing may need more carefully engineered segmentation than a conventional circuit. Study circuit loading, cable topology, transformer allocation, isolation, redundancy, fault propagation and maintainability.
Civil works
Inset fixture installation, ducting, cable trenches, chambers, transformer housings, junction boxes, foundations, drainage and pavement reinstatement all still apply. A sophisticated control system cannot make up for badly positioned field equipment.
Related Guides
LED airfield ground lighting Taxiway lighting systems Junction box and transformer housing AGL design engineeringLighting at a taxiway intersection.
AGL Visual Encyclopedia: Taxiway Intersection Lighting Runway Intersection Lighting Intermediate Holding-Position Lights
Low Visibility, Pilot Responsibilities and Signs
Low visibility
Fog, reduced RVR, complex geometry and simultaneous movements make ground movement harder. The system is an added layer of routing and guidance, not simply brighter taxiway lights.
Pilot responsibilities
Keep a careful lookout and remain responsible for wingtip clearance. Do not continue if there are no green lights ahead or a red stop bar is lit. Do not go beyond the verbal clearance limit without ATC approval.
Signs and markings
Green lights tell the pilot “follow this route”. Signs help answer “where am I?”. Both functions stay valuable, and published procedures advise using signs and markings alongside the lights.
Airport safety context
A dynamic taxiway guidance system is part of the airport's overall surface safety architecture. It should work coherently with ATC, runway holding positions, stop bars, taxiway signs, pavement markings, runway guard lights, A-SMGCS where applicable, low-visibility procedures, vehicle movement control and emergency procedures. The green route should never be considered independently of the rest of the airfield environment.
How the lighting configuration changes under low visibility procedures.
AGL Visual Encyclopedia: Low-visibility procedures (LVP) lighting configuration Mode Changeover Sequence (Normal to LVP and Back) RVR-to-intensity-step control
Follow the Greens Failure Modes
Click a failure to see what to investigate.
No green lights ahead
Do not assume the route is still active. Check:
- Published stopping and ATC-query provisions
- Route cancelled or timed out
- Segment or circuit failure
- Control or communication fault
- Surveillance data lost
Red stop bar remains ON
The aircraft does not proceed unless the approved procedure covers it. Check:
- ATC authorization status
- Interlock state
- Stop-bar control fault
- Communication with field controller
Wrong route illuminated
A potentially serious control issue needing immediate investigation:
- Route logic or data error
- Wrong segment addressing
- Operator selection error
- Conflicting route requests
Multiple green paths
Ambiguity is a safety issue, not a minor lighting fault:
- Overlapping route segments
- Late extinguishing behind aircraft
- Two routes requested together
- Pilot stops and seeks confirmation
Communication failure
The field lighting may need to revert to a defined safe state:
- Network or switch failure
- Field controller offline
- Fallback state defined and tested
Surveillance failure
The system needs an approved response to loss of position data:
- Sensor or data-link loss
- Track loss or false track
- Fallback to manual route control
CCR failure
Affected lighting segments may become unavailable:
- CCR trip or open circuit
- Circuit loading problem
- Segment-to-circuit mapping
- Standby or alternative circuit
Control system failure
Operational procedures should define the fallback method:
- Server or processor fault
- Single point of failure
- Revert to verbal taxi instructions
- Event logging for investigation
Fail-safe design questions
What if a light fails?
Define the effect on the route indication.
What if a stop bar fails?
Define the safe state and the pilot indication.
What if communications fail?
Define the safe state of the field lighting.
What if surveillance is lost?
Define the approved response.
What if two routes are requested?
Define priority and conflict handling.
What if the controller cancels a route?
Define what the pilot sees.
What does the pilot see in degradation?
Define the indication during partial failure.
Is redundancy adequate?
Cover power, processors, links, switches, field controllers and surveillance inputs.
Redundancy matters because a failure here can affect more than one light. It can affect the route-generation function. The level of redundancy should follow the operational role and airport requirements.
What happens when the control system fails.
AGL Visual Encyclopedia: ALCMS Failure Flow Stop Bar Monitoring ALCMS Troubleshooting Flow
Testing and Commissioning
A complete programme tests the system in layers. The aim is to learn what the system does when something goes wrong, not only when everything works.
Field equipment test
Centreline light and stop-bar operation, fixture orientation, physical condition and electrical connections.
Electrical test
Cable condition, insulation, transformers, CCR operation, circuit loading and earthing.
Control test
Individual segment commands, route activation, extinguishing, status feedback and alarms.
Interlocking test
Stop-bar logic, holding-position protection, conflicting routes, route cancellation and fail-safe behaviour.
Surveillance integration test
Where applicable: aircraft position, route tracking, automatic activation and extinguishing, and position-data failure behaviour.
Operational test
Approved operating scenarios with ATC and airport stakeholders.
Photometric test
Verify the optical performance of the installed lighting.
Failure mode test
Deliberately test communication, field-light, control-panel, surveillance, power and stop-bar failures and route conflicts.
Photometry and the Wider Test Programme
Dynamic route selection does not remove the need to verify the optical performance of the underlying lights. Testing may cover intensity, colour, aiming, coverage, configuration, light-unit operation and selected-route performance. This matters most where a large number of centreline fittings is installed as a controllable network.
Useful workflow
Follow the Greens Maintenance
The airport maintains physical AGL infrastructure and dynamic control logic together.
Lighting
- Clean fixtures
- Inspect lenses
- Replace defective fittings
- Inspect transformers
- Inspect connectors
Electrical
- Test circuits
- Inspect insulation
- Verify CCRs
- Inspect field wiring
Control
- Test route commands
- Verify feedback
- Test controller interfaces
- Inspect communications
Operational
- Validate route scenarios
- Test stop-bar interaction
- Test abnormal conditions
Photometry
- Measure optical performance
- Identify deteriorating fittings
- Retest after repairs
Follow the Greens in India
India already has extensive green taxiway centreline lighting. Current AAI eAIP material documents inset bidirectional green centreline lights at Cochin, and unidirectional green lights on rapid-exit taxiways at Hyderabad. The engineering question is therefore not “can green centreline lights be installed?” It is whether the rest of the system can support dynamic routing.
Questions for an Indian airport to answer
Can the AGL network be segmented?
Existing circuits may be too coarse.
Can the ALCMS control individual routes?
Check what the current system can command.
Can stop bars be interlocked?
Review the control architecture.
Is reliable surveillance available?
Aircraft and vehicle position data.
Can the procedure be approved?
Agreement with ATC and the relevant authorities.
Can the whole system be tested and maintained?
Plan for the full life cycle.
Existing airports (retrofit)
A retrofit can be significantly more complex than a new installation.
- Old or shared AGL circuits
- Legacy CCRs and limited segmentation
- Existing stop bars and mixed LED / conventional fittings
- Legacy control panels and incomplete monitoring
- Outdated cable layouts
New airports (greenfield)
Greenfield offers more flexibility and is generally easier than adding routing logic to a legacy network.
- Digital taxiway map with AGL segmentation
- ALCMS, surveillance and stop-bar interlocking designed together
- CCR allocation, circuit topology and communication redundancy
- Power supply, failure modes, manual fallback, maintenance access
Pre-implementation engineering audit
Requirements, Work Packages and Roles
Review before implementing
- Airfield: taxiways, crossings, holding positions, centreline lights, stop bars, signs
- Electrical: CCRs, circuits, transformers, cables, power redundancy
- Control: ALCMS, field controllers, networks, route logic, HMI
- Surveillance: aircraft and vehicle position, accuracy, availability
- Operations: ATC and low-visibility procedures, clearance limits, degraded modes
- Testing: FAT, SAT, integrated, photometry, failure-mode and operational validation
| EPC work package | Scope |
|---|---|
| Civil | Foundations, ducts, chambers, pavement works |
| AGL | Centreline lights, stop bars, fittings |
| Electrical | CCR, transformers, primary circuit, secondary connections |
| Control | ALCMS/ILCMS, PLC/RTU, field controllers, HMI |
| Network | Communication infrastructure |
| Surveillance | Position-data integration where required |
| Testing | Electrical, functional, control, interlock, photometric |
| Commissioning | Integrated operational testing |
Consultant role
Prepare or review the concept of operations, taxiway segmentation, lighting layout, route logic, control architecture, stop-bar interlocking, specifications, communication and surveillance interfaces, fail-safe philosophy, test procedures, acceptance criteria and maintenance philosophy. The key task is defining the boundary between lighting engineering and operational surface-movement control.
Contractor capability
AGL installation, CCR, cabling, stop bars, centreline lights, ALCMS, testing, photometry and commissioning, plus airside construction constraints, closures, work permits, safety controls and coordination with airport operations.
Service scope along the project
Recommended Engineering Workflow
Airport survey
Map existing taxiway and lighting assets.
Operational study
Understand taxi routes and movement requirements.
Lighting design
Develop centreline and stop-bar configuration.
Circuit design
Create electrically controllable segments.
Control architecture
Design ALCMS/ILCMS and field-control interfaces.
Surveillance integration
Define the positional-data interface where required.
Safety logic
Develop route and stop-bar interlocking.
Installation
Execute civil, electrical and AGL works.
FAT
Test control and field equipment before deployment as appropriate.
SAT
Verify installed equipment.
Integrated testing
Test actual route-selection scenarios.
Photometry
Verify lighting performance.
Operational trials
Controlled airport trials.
Handover
Software, drawings, test results, procedures and maintenance documentation.
From survey to handover.
AGL Visual Encyclopedia: Commissioning Sequence ALCMS-to-Taxiway
Benefits and Limitations
Benefits (when properly designed and approved)
- Improved route visibility
- Reduced route ambiguity
- Better support for complex taxiway layouts
- Low-visibility support
- Better integration with ATC
- Active route distinguished from inactive routes
- Lighting becomes an operational tool, not only infrastructure
Limitations
- Cannot replace ATC clearance, pilot lookout, signs, markings, surveillance or approved procedures
- Adds dependencies: control, communications, surveillance, field lighting, power and procedures
- A failure in any critical part can affect the guidance function
- Changi’s procedure, for example, keeps verbal clearance limits and normal positional awareness
Follow the Greens Project Checklist
Click an item to mark it complete.
Concept and design
Installation and testing
Handover
Quick Knowledge Check
Q1. What is the main difference between green centreline lighting and Follow the Greens?
Q2. Do the green lights replace ATC clearance?
Q3. A pilot told to follow the greens sees no green lights ahead. What should happen?
Q4. Why is stop-bar interlocking important?
Q5. Does Follow the Greens remove the need for photometric testing?
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Follow the Greens FAQ
Q1What does “Follow the Greens” mean at an airport?
It is an operational surface-guidance concept in which selected green taxiway centreline light segments are illuminated to give pilots visual guidance along an ATC-cleared taxi route.
Q2Are Follow the Greens and green taxiway centreline lights the same thing?
No. Green centreline lights are the physical visual aid. Follow the Greens is an operational and control concept that dynamically selects and uses those lights.
Q3Does Follow the Greens replace ATC instructions?
No. It works with ATC clearance and an approved procedure. Published airport procedures keep clearance limits and other ATC controls.
Q4Does Follow the Greens work only in low visibility?
Not necessarily. Dubai’s published procedure says its system can provide guidance during, but not only during, low visibility. Singapore Changi’s procedure applies to night operations and periods of low visibility.
Q5What colour are the route lights?
The route indication uses green taxiway centreline lights.
Q6What happens at a runway holding position?
The route generally ends at the protected holding position, where red stop-bar lighting and ATC authorization form part of the control concept. Exact logic depends on the airport’s approved system.
Q7Does the system need aircraft surveillance?
Not in every implementation. Advanced implementations can use aircraft position information to manage the illuminated route automatically, as Dubai’s published system does with ground-surveillance data.
Q8Is Follow the Greens available in India?
India has extensive green taxiway centreline lighting, documented in AAI eAIP material for airports including Cochin and Hyderabad. Whether a particular airport runs a full Follow the Greens procedure needs separate confirmation from its published aeronautical information and approved operational documents.
Q9Does Follow the Greens need ALCMS?
A dynamic implementation needs a control architecture that can select and monitor the required lighting segments. The platform may be an ALCMS, an ILCMS or an integrated surface-movement lighting-control architecture.
Q10Does Follow the Greens require photometric testing?
The underlying taxiway lighting still needs optical performance verification. Dynamic control does not remove the need for AGL testing, inspection and photometry.
Q11What should a pilot do if there are no green lights ahead?
Do not continue taxiing on the assumption the route is still active. Published procedures tell pilots to stop and query ATC.
Q12What if several green segments are visible?
Treat it as ambiguity. Changi’s published procedure tells pilots to stop and seek confirmation before taxiing further.
Engineering & Expert Notes
Guidance Depends on Correct Routing Data
RoutingCheck route definitions and segment configuration, as errors can lead aircraft along the wrong path.
Stop Bars Remain the Control Layer
Stop BarsGreen guidance does not replace clearance. Confirm that red stop bars and procedures interlock correctly.
Test the Whole Chain
IntegrationVerify the link from control to lighting segments to what the pilot sees, including degraded modes.
Check Visibility in Low Visibility Conditions
VisibilityConfirm that the system is usable by flight crews at the intended visibility and spacing.
Plan Failure Responses
Failure ModesDecide in advance what happens when segments fail or data is lost, and brief staff.
Train Controllers and Crews Together
TrainingThe concept relies on shared understanding. Include phraseology and procedures in training.
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