ALSF-2 VS MALSR
High Intensity Approach Lighting System with Sequenced Flashing Lights vs Medium-Intensity Approach Lighting System with Runway Alignment Indicator Lights — both are FAA approach lighting systems, but they are intended for different levels of approach operations. ALSF-2 = High-intensity approach lighting associated with CAT II/III operations. MALSR = Medium-intensity approach lighting, typically associated with CAT I operations.
At a Glance
| Parameter | ALSF-2 | MALSR |
|---|---|---|
| Full form | High Intensity Approach Lighting System with Sequenced Flashing Lights | Medium-Intensity Approach Lighting System with Runway Alignment Indicator Lights |
| Intensity | High | Medium |
| Typical approach association | CAT II / CAT III | CAT I |
| Typical system extent | 2,400–3,000 ft | About 2,400 ft |
| Centreline | Yes | Yes |
| Crossbars / side-row bars | Extensive | Simpler |
| Sequenced flashing | Yes | Yes, through RAIL |
| RAIL | No | Yes |
| Red inner lights | Yes | No |
| Visual guidance | Very high | Moderate |
| System complexity | High | Moderate |
| Electrical infrastructure | More extensive | Simpler |
| Number of light sources | Much higher | Lower |
| Maintenance | Higher | Moderate |
The FAA describes ALSF-2 as a system providing visual information for runway alignment, height perception, roll guidance and horizontal references for CAT II/III approaches.
What Is ALSF-2 & MALSR?
ALSF-2
ALSF-2 stands for High Intensity Approach Lighting System with Sequenced Flashing Lights. It is designed to provide extensive visual guidance during precision instrument approaches.
The FAA describes ALSF-2 as extending into the approach area approximately 2,400–3,000 ft, with a typical system containing 247 steady-burning lights plus 15 flashing lights.
Visual information includes
- Runway alignment
- Height perception
- Roll guidance
- Horizontal references
- Threshold identification
- Sequenced flashing guidance
MALSR
MALSR stands for Medium-Intensity Approach Lighting System with Runway Alignment Indicator Lights. It is installed along the extended runway centreline.
Uses
- Steady-burning light bars
- Threshold lights
- Sequenced flashers / RAIL
The FAA describes MALSR as providing visual information concerning runway alignment, height perception, roll guidance and horizontal references during the visual portion of an instrument approach.
High-Intensity CAT II/III vs Medium-Intensity CAT I
The simplest memory rule:
ALSF-2
HIGH intensity + extensive configuration + sequenced flashers + red side-row lighting
MALSR
MEDIUM intensity + simpler configuration + RAIL
Engineering point: ALSF-2 provides substantially more extensive visual information than MALSR, particularly for low-visibility CAT II/III operations.
High vs Medium Intensity
This is the first major engineering distinction between the two systems.
ALSF-2
High-intensity. The system is designed for demanding precision-approach environments.
MALSR
Medium-intensity. It provides visual approach guidance but with a less extensive lighting configuration.
Note: ALSF-2 ≠ MALSR at a higher intensity setting. They are separate FAA approach-lighting configurations.
Approach Layout, Conceptually
ALSF-2
Outer Approach → Sequenced Flashers → White Centreline → White Side Rows / Crossbars → Red Inner Approach Lights → Threshold → Runway.
The red side-row lights are a major feature distinguishing ALSF-2 from MALSR. FAA's typical ALSF-2 configuration includes green threshold lights, red side-row bars, high-intensity white lights and sequenced flashers.
MALSR
Outer Approach → RAIL Flashers → White Centreline Light Bars → Side Light Bars at the 1,000-ft Station → Threshold → Runway.
The FAA describes MALSR as having nine sets of five steady-burning light sources, with seven centreline bars at 200-ft intervals and two offset bars at the 1,000-ft station, plus five white sequenced flashers.
A Major Difference
ALSF-2
Has red side-row approach lights in the inner portion of the system. These provide additional visual information during the final approach.
MALSR
Does not have the ALSF-2 red side-row configuration. Its visual guidance relies primarily on white steady-burning light bars, threshold lights and RAIL flashers.
Flashing Terminology & Configuration
Both systems use flashing visual guidance, but don't confuse the two systems.
ALSF-2
Uses a more extensive sequenced flashing light system. The flash sequence starts at the outer portion and progresses toward the runway, producing the appearance of a ball of light moving toward the threshold.
MALSR
Uses Runway Alignment Indicator Lights (RAIL). The FAA describes five white flashers in the RAIL array, located at 200-ft intervals, with the flashing producing the appearance of a ball of light traveling toward the runway.
Element-by-Element Comparison
| Feature | ALSF-2 | MALSR |
|---|---|---|
| High-intensity white lights | Yes | No |
| Medium-intensity lights | No | Yes |
| Centreline | Yes | Yes |
| Crossbars / side rows | Extensive | Limited |
| Sequenced flashing | Yes | Yes |
| RAIL terminology | No | Yes |
| Red inner/side-row lights | Yes | No |
| Green threshold lights | Yes | Yes |
| Visual guidance | Extensive | Moderate |
Where Each System Applies
This is the most important operational distinction.
ALSF-2
FAA identifies ALSF-2 with CAT II/III visual guidance.
MALSR
FAA identifies MALSR with CAT I service in its approach-lighting program.
However, the approach category is not determined by the lighting system alone. The complete approach system, aircraft/operator capability, navigation equipment, runway facilities and applicable operating criteria all matter.
Comparable Footprint, Different Configuration
ALSF-2
FAA states that precision approach ALS configurations extend approximately 2,400–3,000 ft, with ALSF-2 commonly using the 2,400-ft portion of the system.
MALSR
MALSR is approximately 2,400 ft in its standard FAA configuration.
The two systems can have similar overall approach-lighting extents, but their internal configurations are very different.
Circuit & Control Design
ALSF-2
Must accommodate a large number of high-intensity fixtures, multiple approach-light circuits, isolation transformers, CCRs, sequenced flashers, red side-row lighting, control and monitoring, and multiple intensity settings.
MALSR
Generally involves medium-intensity fixtures, a series circuit, isolation transformers, a CCR, threshold lighting, a RAIL/flasher circuit, and control and monitoring.
ALSF-2 has a significantly larger electrical and control infrastructure than MALSR. FAA ALCMS guidance separately identifies ALSF/SSALR and MALSR/MALSF interfaces, with different control and monitoring requirements.
What the Designer Must Account For
ALSF-2
- Larger number of fixtures
- Higher fixture intensity
- Multiple circuit loads
- CCR capacity
- Cable length
- Voltage drop
- Transformer losses
- Flasher loads
- Red-light circuit loads
- Intensity control
MALSR
- Medium-intensity fixture load
- Series circuit length
- Transformer rating
- CCR capacity
- RAIL/flasher load
- Cable resistance
- Voltage drop
Multi-Step Intensity Settings
ALSF-2 has more extensive intensity-control requirements. FAA documentation shows ALSF-2 with five steady-burning intensity steps and three flashing-light steps, whereas MALSR uses a simpler intensity arrangement.
This is important for electrical/control engineers because ALSF-2 is not simply an ON/OFF lighting system.
Verification Requirements
ALSF-2
- High-intensity white light output
- Red side-row intensity
- Centreline intensity
- Crossbar/side-row alignment
- Flash intensity
- Flash sequence
- Colour
- Beam orientation
- Threshold lighting
MALSR
- Medium-intensity output
- Centreline alignment
- Crossbar alignment
- RAIL intensity
- Flash sequence
- Colour
- Beam orientation
- Threshold lighting
Maintenance Comparison
| Maintenance Activity | ALSF-2 | MALSR |
|---|---|---|
| Fixture inspection | Required | Required |
| Lens/prism inspection | Required | Required |
| Cable inspection | Required | Required |
| Isolation transformer inspection | Required | Required |
| Insulation resistance | Required | Required |
| Alignment | Required | Required |
| Photometry | Required | Required |
| Flasher testing | Required | Required |
| Flash synchronization | Required | Required |
| Red-light inspection | Required | Not applicable |
| Multiple intensity testing | Extensive | Simpler |
| Control/monitoring | More extensive | Simpler |
Installation Complexity
ALSF-2
Requires coordination of:
- Centreline
- Multiple crossbars/side rows
- Red inner lighting
- High-intensity fixtures
- Sequenced flashers
- Multiple circuits
- CCRs
- Isolation transformers
- Frangible supports
- Approach clearance
MALSR
Requires:
- Centreline
- Light bars
- Offset bars
- RAIL flashers
- Threshold lights
- CCR
- Isolation transformers
- Cable routes
- Frangible supports
MALSR is therefore generally easier to install and maintain.
Positioning Within the FAA ALS Family
| Parameter | MALSR | ALSF-1 | ALSF-2 |
|---|---|---|---|
| Intensity | Medium | High | High |
| Typical category | CAT I | CAT I | CAT II/III |
| Centreline | Yes | Yes | Yes |
| Sequenced flashing | RAIL | Yes | Yes |
| Red inner lights | No | Yes | Yes, more extensive |
| Visual guidance | Moderate | High | Very high |
| Complexity | Moderate | High | Very high |
| Low-visibility role | Lower | Higher | Highest |
Operationally relevant: under 14 CFR 91.175, a pilot using an approach light system as the sole visual reference may not descend below 100 ft above touchdown zone elevation unless the red terminating bar or red side row bars are also distinctly visible and identifiable. ALSF-2's red side row bars provide this reference; MALSR does not have this defining red inner-bar arrangement, so this specific 100-ft allowance does not apply to it in the same way. Always verify against the current regulation text and the specific approach procedure.
Myths vs Facts
No. Their configurations, intensity levels and operational roles are different.
MALSR includes sequenced RAIL flashers.
They are related high-intensity systems, but ALSF-2 has the configuration required for CAT II/III visual guidance.
FAA describes ALSF-2 as providing visual guidance for CAT I, CAT II and CAT III operations.
No. The approach category is determined by the complete operational and approach system.
Choosing Between ALSF-2 and MALSR
When determining ALSF-2 vs MALSR, evaluate:
- Approach category
- Decision height
- RVR/visibility requirements
- Runway operational requirements
- FAA criteria
- Existing ILS/approach system
- Approach-area geometry
- Available land
- Obstacle environment
- Required visual guidance
- Electrical infrastructure
- CCR capacity
- Control and monitoring
- Photometric requirements
From Requirement to Commissioning
Determine approach category → determine visual guidance requirement → identify FAA ALS configuration → select MALSR / ALSF-2 → prepare approach layout → determine light positions → design series circuits → select CCRs → select isolation transformers → design flasher & control system → install fixtures → alignment → electrical testing → intensity testing → flasher testing → photometric verification → commissioning.
Which System Applies Where?
ALSF-2 and MALSR are not interchangeable. ALSF-2 is the substantially more complex, high-intensity system and is associated by FAA with CAT II/III approach operations. MALSR is a medium-intensity system using steady-burning light bars and RAIL flashers, and FAA identifies it with CAT I service.
Final selection should always be based on the applicable FAA design criteria, approach category and approved airport design.
Engineering & Expert Notes
Do Not Treat the Choice as an Upgrade Path Only
SelectionDifferent configurations serve different approach categories. Confirm which one the runway actually needs.
Plan Circuits and Redundancy for the Larger System
ElectricalLow-visibility operations raise reliability expectations. Review circuit design and secondary power.
Include Control and Monitoring in the Comparison
ControlStatus monitoring and flash synchronisation affect operational availability.
Verify Against the Current Standard
ComplianceCheck the current edition and local requirements before final selection.
Frequently Asked Questions
No. ALSF-2 and MALSR are different FAA approach-lighting systems with different intensity levels, configurations and typical CAT associations.
Yes. MALSR includes Runway Alignment Indicator Lights (RAIL), five white flashers at 200-ft intervals that create the appearance of a ball of light traveling toward the runway.
ALSF-2 is the system FAA identifies with CAT II/III visual guidance; MALSR is identified with CAT I service.
ALSF-2 extends approximately 2,400–3,000 ft, while MALSR is approximately 2,400 ft. The exact configuration must follow the applicable FAA design criteria and project layout.
No. FAA describes ALSF-2 as providing visual guidance across CAT I, CAT II and CAT III operations, not CAT III exclusively.
ALSF-2 uses multiple steady-burning and flashing-light intensity steps to suit varying visibility conditions, whereas MALSR uses a simpler intensity arrangement.
Governing Documents
For an actual FAA airport project, verify the current applicable requirements before using this comparison for project design.
FAA VGLS — ALSF-2
FAA's Visual Guidance Lighting Systems page for the High Intensity Approach Lighting System with Sequenced Flashing Lights (ALSF-2) — configuration, fixture counts and CAT II/III role.
FAA VGLS — MALSR
FAA's Visual Guidance Lighting Systems page for the Medium Intensity Approach Light System with Runway Alignment Indicator Lights (MALSR) — light bar layout, RAIL array and CAT I role.
FAA Approach Lighting System Improvement Program (ALSIP)
Congressional program guidance describing the FAA's approach-lighting system inventory and associated approach categories.
AC 150/5345-56B — ALCMS
Specification for L-890 Airport Lighting Control and Monitoring System, covering separate ALSF/SSALR and MALSR/MALSF interfaces and control/monitoring requirements.
ALSF-2 = High Intensity + CAT II/III + Red Side Rows + Extensive Sequenced Flashing. MALSR = Medium Intensity + CAT I + RAIL.
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