Stop Bar VS Clearance Bar
Stop Control vs Position Reference — a Stop Bar is a row of red lights that gives a positive command to stop and not proceed, while a Clearance Bar is a row of yellow lights that identifies a clearance or holding position rather than commanding a stop. One controls movement; the other marks a position the pilot must recognise and respect.
At a Glance
| Feature | Stop Bar | Clearance Bar |
|---|---|---|
| Main purpose | Stop and prevent further movement | Mark/identify a clearance or holding position |
| Colour | Red | Yellow |
| Basic message | STOP — do not cross | Clearance/holding position here |
| Typical location | Across taxiway at a runway/intersection holding position | At a clearance/holding position |
| Function | Positive stop indication | Position identification |
| Pilot action | Stop when illuminated | Recognise the position and comply with applicable clearance/procedure |
| Primary safety role | Direct movement control | Separation/position awareness |
| Typical fixture | Inset | Inset/elevated depending on installation |
Control vs Reference
Both fixtures can sit along the same taxiway route, but they carry different weight in a pilot's decision-making. A Stop Bar is a transverse row of red lights across the taxiway — when illuminated its message is unambiguous: stop, do not proceed across the bar. A Clearance Bar is a line of yellow lights used to identify a clearance or holding position, helping the pilot recognise where they are relative to the protected area rather than issuing a stop command.
What Is Each Light?
Stop Bar
A transverse row of red lights across the taxiway at a holding position, forming a clear, positive visual restriction on movement.
Tells the pilot
- Stop — do not proceed across the bar
- The restriction applies when the bar is illuminated
- Its significance is particularly important at runway holding positions and other protected locations
Clearance Bar
A line of yellow lights used to identify a clearance/holding position, functioning as a reference line rather than a stop command.
Tells the pilot
- A defined clearance/holding position is here
- Recognise the position and follow applicable taxi/ATC instructions
- It helps identify where the aircraft should be positioned relative to the protected/movement area
Red = Stop · Yellow = Clearance/Caution
This is the fastest way to tell the two apart. The Stop Bar provides a direct stop indication — a visual barrier the pilot must not cross while it is illuminated. The Clearance Bar provides a position reference — it identifies where the clearance or holding position is, without itself issuing a stop command.
Stop Bar = stop control. Clearance Bar = position/clearance reference. Easy memory: red = stop, yellow = clearance/caution.
These Are Not Interchangeable Lights
Do not confuse the two: an illuminated Stop Bar prohibits crossing — the aircraft must stop before it. A Clearance Bar does not carry the same stop instruction; it identifies a position, and crossing it is governed by applicable procedures rather than being outright prohibited. Each provides a different operational function in a controlled movement area.
How Each Reads From the Cockpit
Stop Bar
The aircraft stops before the illuminated bar. Think of the Stop Bar as a visual barrier: do not pass while it is lit.
Clearance Bar
The pilot recognises a defined position and follows the applicable taxi/ATC instructions. Think of the Clearance Bar as a reference line, not a barrier.
Stop Bar vs Clearance Bar
| Parameter | Stop Bar | Clearance Bar |
|---|---|---|
| Colour | Red | Yellow |
| Primary function | Stop/control | Position identification |
| Visual meaning | Do not proceed | Clearance/holding reference |
| Direct stop indication | Yes | No |
| Crossing while illuminated | Prohibited | Governed by applicable procedures |
| Main safety function | Prevent unauthorized movement | Maintain appropriate clearance/position |
| Pilot emphasis | Stop | Position/clearance |
Common Terminology Confusion
It does not carry the same stop command. The clearance bar identifies a clearance/holding position; the pilot recognises the position and complies with the applicable procedure or ATC instruction, rather than treating it as an automatic stop.
Each provides a different operational function. The stop bar controls movement with a positive red stop indication, while the clearance bar is a yellow position reference — one does not substitute for the other.
Colour carries the operational meaning directly — red is the universal stop indication, and yellow signals clearance or caution rather than an outright prohibition.
Stop Bar vs Clearance Bar
The fundamental difference is stop control versus position reference. Both can appear along the same taxi route toward a runway or intersection, but they carry different weight in the decision to proceed.
The Stop Bar controls movement — stop and do not cross when illuminated. The Clearance Bar identifies the required clearance/holding position — recognise it and follow the applicable procedure.
Easy memory: Stop Bar → stop, do not cross. Clearance Bar → position, maintain clearance.
Engineering & Expert Notes
Do Not Treat Them as Interchangeable
PrincipleThey have different meanings and rules.
Test Control and Interlock for Stop Bars
ControlVerify switching.
Inspect at Night
InspectionCheck for gaps.
Keep Records of Layout and Configuration
RecordsUpdate with changes.
Frequently Asked Questions
Function and colour — the stop bar is a red row of lights giving a positive stop command that must not be crossed while illuminated, while the clearance bar is a yellow row of lights identifying a clearance or holding position without itself commanding a stop.
No. Crossing an illuminated stop bar is prohibited — it forms a positive visual barrier at the holding position.
Not in the same way as a stop bar. The clearance bar identifies a clearance/holding position, and crossing it is governed by applicable procedures rather than being an automatic prohibition.
The stop bar is typically installed across the taxiway at a runway or intersection holding position. The clearance bar is installed at a clearance/holding position and may be an inset or elevated fixture depending on the installation.
Red universally signals stop, while yellow signals clearance or caution — so the colour alone communicates whether the fixture is a stop control or a position reference.
Governing Documents
For an actual project design, always verify the current edition of the applicable documents.
ICAO Annex 14, Volume I
Aerodrome Design and Operations — stop bar and clearance bar colour, siting, configuration and operational requirements at holding positions.
FAA AC 150/5340-30
Design and Installation Details for Airport Visual Aids — stop bar and clearance bar configuration, installation and electrical systems.
FAA AC 150/5345-46
Specification for Runway, Taxiway, Heliport, and Vertiport Light Fixtures — governs the L-852 series in-pavement fixtures used for stop bars and clearance/caution bars.
DGCA / AAI Requirements
For Indian airport projects, also verify applicable DGCA requirements, AAI requirements, airport-specific technical specifications, project drawings and contract specifications.
Final Engineering Note
Do not design a stop bar or clearance bar arrangement from a generic web diagram. The final installation drawing should always be developed from the current governing standard, approved airport design and project-specific requirements.
Stop bar = red positive stop indication that must not be crossed while illuminated. Clearance bar = yellow position reference that identifies a clearance/holding position.
Compare the Systems. Then Learn How to Engineer Them.
Understanding the difference between AGL systems is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
Build Practical AGL Engineering Skills
Go deeper with structured training from Precision AGL Academy, covering:
Learn how AGL systems work as part of a complete airport lighting system, not just as individual components or configurations.