MALS VS MALSF
Medium Approach Lighting System vs Medium Approach Lighting System with Sequenced Flashing Lights — both are FAA medium-intensity approach lighting systems that provide visual guidance during the transition from instrument approach to visual runway acquisition. MALS is the basic medium-intensity arrangement. MALSF adds three sequenced flashers on top of the same 1,400 ft base configuration.
MALS vs MALSF at a Glance
| Parameter | MALS | MALSF |
|---|---|---|
| Full form | Medium Approach Lighting System | Medium Approach Lighting System with Sequenced Flashing Lights |
| System type | Medium-intensity approach lighting | Medium-intensity approach lighting |
| Primary function | Runway alignment and threshold acquisition | Runway alignment, threshold acquisition and sequenced visual cue |
| Intensity | Medium | Medium |
| Approach centreline | Yes | Yes |
| Crossbar | Yes — 1,000 ft crossbar | Yes — 1,000 ft crossbar |
| Sequenced flashing lights | No | Yes — three flashers at the last three light-bar stations |
| Flashing sequence control | Not applicable | Required |
| Visual guidance | Basic / moderate | Enhanced |
| Electrical complexity | Lower | Higher |
| Control complexity | Lower | Higher |
| Maintenance | Lower | Higher |
| Typical system length | 1,400 ft (427 m) | 1,400 ft (427 m) |
| Minimum land requirement | 1,600 × 400 ft | 1,600 × 400 ft |
| Typical application | Nonprecision approach | Nonprecision approach where approach-area identification is difficult (e.g. high ambient background lighting) |
| New FAA installation | No longer installed as a new FAA facility | Still a listed configuration in FAA JO 6850.2C |
What Is MALS & MALSF?
MALS
MALS stands for Medium Approach Lighting System. It is a medium-intensity approach lighting system used to provide visual guidance to pilots during the final portion of an approach. In the FAA configuration it has a green threshold bar and seven five-lamp light bars on the extended runway centreline at 200 ft spacing (out to 1,400 ft), plus a crossbar at 1,000 ft, giving a visual extension of the runway centreline into the approach area. MALS has no sequenced flashers, and the FAA no longer installs it as a new facility.
Primary functions
- Runway alignment
- Centreline identification
- Threshold acquisition
- Transition from instrument to visual flight
MALSF
MALSF stands for Medium Approach Lighting System with Sequenced Flashing Lights. It combines the basic medium-intensity approach lighting arrangement with sequenced flashing lights. Three sequenced flashers, fitted at the last three light-bar stations, flash in turn toward the threshold twice per second. This creates an apparent movement of light toward the runway and gives the pilot an additional directional cue, which is most useful where the approach area is hard to pick out against high ambient background lighting.
This helps the pilot
- Recognize runway direction
- Establish approach alignment
- Locate the runway environment
- Transition from instrument to visual flight
The Main Difference
The easiest way to remember the difference between MALS and MALSF:
MALS
Medium intensity + steady approach lighting
MALSF
Medium intensity + steady approach lighting + sequenced flashers
Memory rule: MALS = MALS without F. MALSF = MALS + F (Flashing).
Visual Guidance Comparison
MALS
Seven steady centreline bars, a 1,000 ft crossbar and a green threshold bar. The system provides a steady visual reference toward the runway.
MALSF
The same steady centreline bars, crossbar and threshold bar as MALS, plus three sequenced flashers at the outer stations that flash in turn toward the threshold. The flashing sequence provides an additional directional cue.
Element-by-Element Comparison
| Feature | MALS | MALSF |
|---|---|---|
| Medium-intensity lights | Yes | Yes |
| Approach centreline | Yes | Yes |
| Crossbar | Yes — 1,000 ft | Yes — 1,000 ft |
| Sequenced flashers | None | Three |
| Flasher control unit | No | Yes |
| Flash synchronization | No | Yes |
| Steady-burning lights | Yes | Yes |
| Threshold reference | Yes | Yes |
Why Add Sequenced Flashers?
The main purpose of the sequenced flashers is to create a strong directional visual cue, especially where the approach area is hard to identify against high ambient background lighting. MALSF has three flashers, fitted at three light-bar stations, and they flash in sequence toward the threshold twice per second. Conceptually: outermost flasher → middle flasher → innermost flasher → runway threshold, repeating continuously.
The apparent movement toward the threshold helps the pilot recognize:
- Runway direction
- Approach alignment
- Runway location
- Transition from instrument to visual flight
Engineering point: This is the major functional advantage of MALSF over MALS.
Electrical Engineering Comparison
| Parameter | MALS | MALSF |
|---|---|---|
| FAA-standard power arrangement | Voltage-fed via power/control equipment | Voltage-fed via power/control equipment |
| CCR series circuit | Only if the approved design specifies it | Only if the approved design specifies it |
| Isolation transformers | Applicable | Applicable |
| Primary cable | Required | Required |
| Secondary connection | Required | Required |
| Flasher circuit | No | Yes |
| Flasher controller | No | Yes |
| Synchronization | No | Yes |
| Control wiring | Simpler | More complex |
| Circuit loading | Lower | Higher |
| Brightness steps | 3 steady (100 / 20 / 4 %) | 3 steady (100 / 20 / 4 %) + 3 flasher (100 / 10 / 2.3 %) |
Simplified path (FAA-standard arrangement) — MALS: power supply → power & control equipment (three-step intensity) → steady-burning light units. MALSF adds sequenced flasher control; the flashers must be on only while the steady-burning lights are on. Where an airport design instead specifies a CCR series circuit, the exact electrical architecture must follow the approved design.
Power Supply & Circuit Considerations
For both systems, the supply and circuit arrangement should be based on the actual connected load (with a CCR only where the approved design specifies a series circuit). Consider:
- Number of fixtures
- Fixture wattage
- Isolation transformer rating
- Circuit length
- Cable resistance
- Voltage drop
- Supply / CCR capacity (as applicable)
- Intensity steps
- Control arrangement
For MALSF, the flashing equipment and its associated electrical/control requirements must also be considered.
Photometric Verification
MALS — Verify
- Light intensity
- Colour
- Beam distribution
- Centreline alignment
- Crossbar alignment
- Fixture orientation
MALSF — All MALS Checks, Plus
- Flash intensity
- Flash sequence
- Flash timing
- Synchronization
- Flasher operation
A MALSF installation can have all steady lights functioning correctly while still having a sequenced-flasher fault.
Installation Considerations
Both systems require coordination of:
- Runway centreline
- Threshold location
- Approach centreline
- Light-unit spacing
- Crossbars
- Mounting structures
- Frangible supports
- Primary cables
- Isolation transformers
- Drainage
- Earthing/bonding where applicable
MALSF additionally requires:
- Flasher equipment
- Flasher controller
- Control wiring
- Synchronization
- Appropriate equipment locations
Maintenance Comparison
| Maintenance Activity | MALS | MALSF |
|---|---|---|
| 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 | Required | Required |
| Photometry | Required | Required |
| Flasher testing | Not applicable | Required |
| Flash synchronization | Not applicable | Required |
| Flasher controller inspection | Not applicable | Required |
MALSF therefore has an additional maintenance layer associated with the flashing system.
MALS vs MALSF: The Simple Version
Think: MALS
"Steady approach lights → Runway."
Think: MALSF
"Steady approach lights + sequenced flashing → Runway."
The additional flashing function gives MALSF a stronger visual directional cue.
Positioning Within the FAA ALS Family
This is useful because these three FAA terms are often confused.
| System | Intensity | Defining Feature |
|---|---|---|
| MALS | Medium | Medium-intensity approach lighting, 1,400 ft, steady-burning only |
| MALSF | Medium | Three sequenced flashing lights, 1,400 ft |
| MALSR | Medium | Runway Alignment Indicator Lights (five RAIL flashers beyond the MALS portion), 2,400 ft |
Easy memory rule: MALS → Medium Approach Lighting. MALSF → MALS + Sequenced Flashing. MALSR → MALS + Runway Alignment Indicator Lights.
Medium vs High Intensity Systems
| System | Intensity | Flashing Feature | General Character |
|---|---|---|---|
| MALS | Medium | No defining sequenced flashing | Simplified medium-intensity approach lighting |
| MALSF | Medium | Sequenced flashing | Medium-intensity approach lighting with flashers |
| MALSR | Medium | RAIL | Medium-intensity approach lighting with runway alignment indicators |
| ALSF-1 | High | Sequenced flashing | High-intensity precision approach lighting (existing configuration; JO 6850.2C lists ALSF-2 as the current high-intensity system) |
| ALSF-2 | High | Sequenced flashing | High-intensity CAT II/III approach visual guidance |
This makes the important distinction clear: MALS/MALSF/MALSR → Medium intensity, while ALSF-1/ALSF-2 → High intensity.
Myths vs Facts
MALSF adds a sequenced flashing-light function to the medium-intensity approach system.
MALS has seven five-lamp light bars on the extended runway centreline, plus a 1,000 ft crossbar.
MALSF is a medium-intensity approach lighting system.
Both use sequenced flashing concepts, but they differ significantly in intensity and overall configuration.
Both are medium-intensity systems with sequenced flashers, but MALSR is a 2,400 ft system (MALS plus five RAIL flashers beyond it) while MALSF is a 1,400 ft MALS with three flashers.
Choosing Between MALS and MALSF
Before selecting MALS or MALSF, verify:
- Approach category
- Runway operational requirement
- Applicable FAA criteria
- Airport-specific specification
- Required visual guidance
- Approach area availability
- Existing ALS configuration
- Power supply / CCR capacity
- Circuit arrangement
- Flasher requirement
- Control and monitoring
- Photometric requirements
The system should be selected from the approved airport design, not simply from the name of the ALS.
From Requirement to Commissioning
Determine approach requirement → identify applicable FAA ALS → select MALS/MALSF → prepare approach layout → determine light positions → design power supply and circuit arrangement → select power/control equipment → select transformers as specified → design cabling → (MALSF) design sequenced flasher system → install fixtures → alignment → electrical testing → flasher functional testing → photometric testing → commissioning.
Which System Applies Where?
MALSF is a medium-intensity approach lighting system incorporating sequenced flashing lights, while MALS is the basic medium-intensity approach lighting system without that defining sequenced-flasher feature.
The addition of sequenced flashing provides an enhanced directional visual cue, but MALSF should not be treated as simply a "higher category" version of MALS. Approach category, operational minima and the complete aerodrome lighting system must be established independently from the ALS name.
Engineering & Expert Notes
Check Flasher Controllers and Timing
SequenceConfirm sequence and synchronisation after maintenance.
Verify Layout and Aiming
LayoutCheck positions and elevation against the design.
Walk the Pattern at Night
InspectionLook for gaps or dim lights.
Stock Flash Heads and Controllers
SparesKeep spares for the flasher parts.
Frequently Asked Questions
No. MALS does not have sequenced flashing lights as a defining feature — it uses steady-burning medium-intensity approach lights.
No. MALSF is the same medium-intensity base arrangement as MALS, with a sequenced flashing-light function added.
No. Both use sequenced flashing, but MALSF is a medium-intensity system while ALSF-1 is a high-intensity precision approach lighting system with a different configuration.
Both are medium-intensity systems that use sequenced flashers. MALSF is a 1,400 ft MALS with three flashers at its outer stations; MALSR is a 2,400 ft system in which five RAIL flashers extend the MALS out by a further 1,000 ft.
The steady lights alone don't provide the intended directional cue, so a MALSF installation can pass a basic visual check while still having a sequenced-flasher fault that needs separate verification.
No. Both MALS and MALSF are medium-intensity approach lighting systems. The difference is the presence of sequenced flashing lights, not intensity level.
Both are 1,400 ft (427 m) systems, needing land at least 1,600 ft long by 400 ft wide. The FAA no longer installs MALS as a new facility.
Three sequenced flashers, fitted at three light-bar stations, flashing in sequence toward the threshold twice per second. They must be on only while the steady-burning lights are on.
Governing Documents
For an actual FAA airport project, verify the current applicable requirements before using this comparison for project design.
FAA Order JO 6850.2C — Visual Guidance Lighting Systems
Installation criteria for FAA approach lighting systems: MALS/MALSF configuration and dimensions (1,400 ft, 1,000 ft crossbar), sequenced-flasher requirements, brightness steps, control requirements and equipment specifications.
FAA AC 150/5340-30 (current edition: J)
Design and Installation Details for Airport Visual Aids — installation guidance for airport visual aids including MALSF, frangibility and electrical installation practice.
Airport-Specific Technical Specifications
Project drawings and contract specifications control exact light-unit positions, tolerances, flash characteristics, mounting and circuit arrangements. Confirm the current revision of each FAA document before use.
Applicability Note
These are FAA-defined systems. On ICAO/DGCA-regulated aerodromes (including Indian airports), approach lighting is specified as simple or precision (CAT I/II/III) approach lighting under ICAO Annex 14 Volume I, so FAA names such as MALS, MALSF, MALSR and ODALS do not apply directly.
MALS = 1,400 ft medium-intensity steady-burning approach lighting. MALSF = MALS + three sequenced flashers.
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