SALS VS SSALS
Simple Approach Lighting System vs Simplified Short Approach Lighting System — both are simplified approach lighting arrangements used where a full-length precision approach lighting system is not required or cannot be provided. The main difference lies in the configuration, length and level of visual guidance provided toward the runway threshold.
At a Glance
| Parameter | SALS | SSALS |
|---|---|---|
| Full form | Simple Approach Lighting System | Simplified Short Approach Lighting System |
| System type | Simplified approach lighting | Shortened simplified approach lighting |
| Primary purpose | Provide visual alignment and runway acquisition | Provide basic visual guidance where a shorter system is appropriate |
| System length | Longer than SSALS | Shorter than SALS |
| Centreline | Yes | Yes |
| Crossbars | Applicable | Simplified configuration |
| Visual guidance | Moderate | Basic |
| Infrastructure | Moderate | Lower |
| Installation complexity | Moderate | Lower |
| Maintenance | Moderate | Lower |
| Suitable application | Where additional approach visual guidance is required | Where site constraints or operational requirements favour a shorter system |
What Is SALS & SSALS?
SALS
SALS stands for Simple Approach Lighting System — note that some sources, including certain FAA/pilot references, use "Short Approach Lighting System" for the same acronym; both refer to the same system. It is a simplified approach lighting arrangement intended to provide the pilot with visual references during the final stage of an instrument approach. The system provides a visual extension of the runway centreline into the approach area. Compared with a full precision approach lighting system, SALS has a simpler configuration.
Main functions
- Runway alignment
- Centreline identification
- Runway threshold acquisition
- Visual transition from instrument to visual flight
SSALS
SSALS stands for Simplified Short Approach Lighting System. It provides a shorter and simpler approach-lighting arrangement than a conventional SALS. The objective remains the same — supporting the transition from instrument approach through approach lighting to runway visual acquisition and landing — but the available visual information is provided over a shorter approach distance.
Main functions
- Basic centreline guidance
- Threshold acquisition
- Runway alignment
- Visual transition
Simple + Longer vs Simplified + Shorter
The easiest way to remember the difference between SALS and SSALS:
SALS
Simple + Longer visual reference
SSALS
Simplified + Shorter visual reference
Engineering point: The difference between SALS and SSALS is primarily associated with the extent and configuration of the approach lighting system — not a fundamentally different visual philosophy.
Element-by-Element Comparison
| Configuration Element | SALS | SSALS |
|---|---|---|
| Approach centreline | Yes | Yes |
| Crossbars | May be provided according to applicable configuration | Simplified |
| Approach light units | More extensive | Fewer |
| Approach coverage | Longer | Shorter |
| Visual reference | Greater | More limited |
| System complexity | Moderate | Low |
| Installation footprint | Larger | Smaller |
Why Use a Simplified Approach Lighting System?
A full-length approach lighting system may not always be practical. Possible reasons include:
- Terrain
- Obstacles
- Available land
- Existing infrastructure
- Airport layout
- Runway approach category
- Operational requirements
- Cost
- Environmental constraints
A simplified system can provide useful visual guidance without requiring the complete installation associated with a more extensive approach lighting system.
How Each System Guides the Pilot
SALS visual function
SALS provides the pilot with a visual continuation of the runway centreline, helping establish alignment, threshold acquisition and the transition from instrument references to visual runway references.
- Alignment — the centreline helps identify the runway direction
- Threshold acquisition — the approach lighting helps locate the runway threshold
- Transition — supports the shift from instrument to visual runway references
SSALS visual function
SSALS performs the same fundamental function but over a shorter approach area, so the amount of visual information available before threshold acquisition is reduced.
- Basic centreline guidance
- Threshold acquisition
- Runway alignment
- Visual transition
Full Engineering Parameters
| Engineering Parameter | SALS | SSALS |
|---|---|---|
| Visual coverage | Greater | Lower |
| Number of light positions | Higher | Lower |
| Civil works | Moderate | Lower |
| Cable installation | Moderate | Lower |
| Circuit complexity | Moderate | Lower |
| Maintenance points | More | Fewer |
| Land requirement | Higher | Lower |
| Obstacle clearance coordination | Important | Important |
| Installation cost | Generally higher | Generally lower |
| Visual guidance | Better | Basic |
Electrical Considerations
From an AGL engineering perspective, both systems require proper design of the series circuit, CCR, isolation transformers, primary and secondary cable, connectors, junction boxes, control and monitoring, and earthing/bonding where applicable.
Simplified circuit architecture: CCR → Primary Series Circuit → Isolation Transformers → Approach Light Fixtures. The actual circuit architecture depends on the applicable airport design and equipment requirements.
SALS vs SSALS Circuit Considerations
Because SALS normally has a greater number of lighting positions, the circuit designer must consider:
- Total fixture load
- Isolation transformer ratings
- Circuit length
- Cable resistance
- Voltage drop
- CCR rating
- Number of series-circuit loads
- Transformer losses
- Insulation resistance
SSALS generally has fewer lighting positions, which can simplify the circuit and reduce the physical installation.
A shorter system does not automatically mean a different CCR architecture. The final electrical design must be calculated from the actual fixture ratings and approved circuit configuration.
Photometric Considerations
Both SALS and SSALS should be checked against the applicable photometric requirements. Verification may include:
Intensity
Confirm that each light unit provides the required output.
Alignment
- Horizontal aiming
- Vertical aiming
- Centreline alignment
Colour
Verify that the applicable light colour is correct.
Uniformity
Check the overall visual pattern of the approach lighting system.
Installation Considerations
Before installation, the following should be coordinated: runway centreline, threshold location, approach centreline, light-unit spacing, crossbar position, fixture orientation, mounting height, frangible supports, cable routes, isolation transformer locations, drainage, earthing/bonding and the obstacle environment.
For SSALS, the reduced length can make the system more suitable where the available approach area is limited.
Maintenance Comparison
| Maintenance Activity | SALS | SSALS |
|---|---|---|
| Fixture inspection | Required | Required |
| Lens/prism inspection | Required | Required |
| Water-ingress inspection | Required | Required |
| Cable inspection | Required | Required |
| Isolation transformer inspection | Required | Required |
| Insulation resistance | Required | Required |
| Alignment check | Required | Required |
| Photometry | Required | Required |
| Structural/frangible inspection | Required | Required |
The main difference is the number of components and physical coverage, not the fundamental maintenance philosophy.
SALS vs SSALS vs Full Approach Lighting
| System | General Character |
|---|---|
| Full precision ALS | Extensive visual guidance for precision approaches |
| SALS | Simplified approach lighting |
| SSALS | Shorter simplified approach lighting |
| No ALS | No dedicated approach-lighting visual extension |
Progression: Full ALS → SALS → SSALS → No approach lighting. As the system becomes simpler, the available visual information generally decreases.
Practical Difference
Think: SALS
Simple + more approach coverage
Think: SSALS
Simplified + shorter approach coverage
Myths vs Facts
The primary distinction is the configuration and shorter extent of the system, not simply light intensity.
SSALS still provides visual approach guidance, but over a shorter and simplified configuration.
They are different approach-lighting configurations and should not be treated as interchangeable with FAA ALSF classifications.
Approach category and approach-lighting configuration are separate concepts. The applicable aerodrome standard determines the permitted combination.
Choosing Between SALS and SSALS
When selecting between SALS and SSALS, consider:
- Approach category
- Runway operational requirements
- Applicable ICAO requirements
- National CAA requirements
- Airport-specific specifications
- Available approach area
- Terrain
- Obstacles
- Land availability
- Required visual guidance
- Electrical infrastructure
- Maintenance requirements
From Requirement to Commissioning
Determine approach requirement → identify applicable standard → select SALS/SSALS configuration → prepare approach layout → determine light positions → design series circuit → select CCR → select isolation transformers → design primary & secondary cabling → install fixtures → alignment → electrical testing → photometric testing → commissioning.
Which System Applies Where?
SALS and SSALS are simplified approach-lighting concepts used where a full-length precision approach lighting system is not required or cannot be provided. Their key distinction is the extent and configuration of visual guidance provided before the runway threshold.
The final selection should always be based on the current applicable ICAO/national standard, approach category, runway requirements and approved airport design — not on a generic comparison alone.
Engineering & Expert Notes
Check Available Space and Obstacles
SiteVerify what the site allows before selecting.
Verify Aiming and Positions
AlignmentRecord as-built data.
Inspect at Night
InspectionCheck for gaps.
Document the Basis for Selection
RecordsKeep a record of the reasons.
Frequently Asked Questions
No. The primary distinction is the configuration and shorter extent of the system, not light intensity.
The overall length and extent of visual coverage provided toward the runway threshold, along with the resulting number of light positions and installation footprint.
Yes. Both SALS and SSALS provide an approach centreline reference; SSALS does so with a simplified configuration.
Not automatically. Approach category and approach-lighting configuration are separate concepts governed by the applicable aerodrome standard.
No. They are different, simplified approach-lighting configurations and should not be treated as interchangeable with FAA ALSF classifications.
Generally SSALS has lower installation cost and fewer maintenance points due to fewer light positions, but final selection must follow the applicable standard and approved airport design rather than cost alone.
Governing Documents
For an actual airport project, verify the current applicable editions of the relevant standards before using this comparison for project design.
ICAO Annex 14, Volume I
Aerodrome Design and Operations — approach lighting systems, simplified configurations, light characteristics, configuration, installation and operational requirements.
ICAO Aerodrome Design Manual
Applicable material covering approach lighting system design, dimensional criteria and configuration guidance.
National CAA / 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
SALS and SSALS terminology and exact dimensional/configuration requirements can vary with the governing standard. For final design, use the configuration drawings and dimensional criteria from the applicable current standard rather than a generic comparison page.
SALS and SSALS are simplified approach-lighting concepts. Their key distinction is the extent and configuration of visual guidance provided before the runway threshold.
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