Approach Lighting System versus Runway Lighting System
An Approach Lighting System (ALS) and runway lighting do different jobs. The ALS starts at the landing threshold and extends outward along the extended runway centreline, helping the pilot line up with the runway during the change from instrument to visual flight. Runway lighting (edge, threshold, runway-end, centreline and touchdown-zone lights) marks the runway itself for landing, rollout and take-off. In FAA guidance they are separate systems with separate installation criteria and separate controls.
Technical review: 20 September 2026, checked against FAA Order JO 6850.2C, FAA AC 150/5340-30J and FAA AIM Chapter 2, Section 1. System names and dimensions on this page follow FAA practice; see section 22 for ICAO/DGCA differences.
At a Glance
| Parameter | Approach Lighting System (ALS) | Runway Lighting |
|---|---|---|
| Primary location | Starts at the landing threshold and extends outward along the extended runway centreline | On and along the runway: edges, threshold, runway end, centreline, touchdown zone |
| Typical extent | 2,400 ft (3,000 ft if the glide slope is below 2.75°) on precision runways; about 1,400 ft on non-precision runways | Edge and end lights along the full runway; touchdown-zone lights to 3,000 ft or mid-runway; centreline lights along the full runway |
| Primary purpose | Runway alignment, roll, height and distance cues during the instrument-to-visual transition | Marks the usable runway limits and guides landing, rollout and take-off |
| Main visual reference | Extended runway centreline with light bars and crossbars | Runway edges, threshold, runway end, centreline, touchdown zone |
| Pilot phase | Final approach, at the transition to visual reference | Late final, landing, rollout and take-off |
| Typical FAA systems | ALSF-2, MALSR, MALSF, SSALR mode (legacy or no longer installed new: ALSF-1, MALS, ODALS) | LIRL, MIRL, HIRL, threshold and end lights, runway centreline lights, touchdown-zone lights |
| Threshold lights | Includes its own green threshold bar at the landing threshold | Yes: green to arriving aircraft, red to departing aircraft at the runway end |
| Runway edge lights | No | Yes: white, with a yellow caution zone on instrument runway ends (MIRL/HIRL) |
| Runway centreline lights | No. The ALS centreline is the extended centreline outside the runway | Yes, where required |
| Touchdown-zone lights | No | Yes, where required |
| Sequenced flashing | Some types (ALSF-2, MALSF, MALSR, SSALR) | No |
| RAIL | MALSR and SSALR only | No |
| Typical power circuit | ALSF-2: 6.6 A / 20 A series circuit fed by a CCR. MALS, MALSF, MALSR: 120/240 V constant-voltage supply | HIRL, MIRL, centreline and touchdown-zone lights: series circuit fed by a CCR. LIRL: usually parallel |
| FAA installation criteria | FAA Order JO 6850.2C. Economy aids (MALSF/MALS, ODALS) also in AC 150/5340-30J, Chapter 7 | AC 150/5340-30J: Chapter 2 (edge, threshold, end) and Chapter 3 (centreline, touchdown zone) |
| Main objective | Find and align with the runway | Identify and use the runway safely |
What Is an Approach Lighting System?
An Approach Lighting System (ALS) is a set of signal lights arranged symmetrically about the extended runway centreline. It starts at the landing threshold and extends outward into the approach area. It gives the pilot visual information on runway alignment, height perception, roll guidance and horizon reference, and it is the basic means of moving from instrument flight to visual flight for landing (FAA AIM 2-1-1; FAA Order JO 6850.2C).
Aircraft → Approach lighting → Threshold → Runway.
Because the ALS lies outside the runway pavement, it is designed around an approach light plane at threshold elevation that must stay clear of obstructions. Runway lighting is designed around the runway geometry.
What Is a Runway Lighting System?
A runway lighting system provides visual references on and along the runway itself. Edge lights mark the lateral limits of the usable landing area. Threshold and runway-end lights mark its longitudinal limits. On selected precision runways, centreline and touchdown-zone lights add guidance for landing, rollout and take-off (AC 150/5340-30J, Chapters 2 and 3).
Threshold → Runway → Runway end. The lighting tells the pilot: "This is the runway and this is where I can land, roll, or take off."
The Simplest Difference
Approach Lighting
Before the runway: "Where is the runway and how am I aligned with it?"
Runway Lighting
On the runway: "Where are the runway limits and where is the usable runway surface?"
Common FAA Approach Lighting Systems
High-Intensity
- ALSF-2: Approach Lighting System with Sequenced Flashing Lights, CAT II/III configuration. Five steady-burning brightness steps and three flasher intensities.
- ALSF-1: legacy high-intensity configuration. It still appears on charts and at some older or military sites, but it is not among the systems described in the current FAA Order JO 6850.2C.
Medium-Intensity
- MALSR: MALS plus RAIL (five sequenced flashers) out to 2,400 ft. The typical CAT I system.
- SSALR: charted as a standalone system at many airports. FAA now treats it as the medium-intensity mode of the dual-mode ALSF-2/SSALR, not as a new standalone installation.
- MALSF: 1,400 ft MALS with three sequenced flashers, for non-precision runways where the approach area is hard to identify.
- MALS: 1,400 ft, no flashers. FAA no longer installs it as a new facility.
Related Visual Guidance Aids
- ODALS: seven omnidirectional flashing lights (five on the extended centreline to 1,500 ft, two at the threshold) for non-precision runways. FAA no longer installs it as a new facility.
- REIL: a pair of synchronised flashing lights, one each side of the threshold, that identify the approach end of the runway. FAA lists REIL as a separate visual guidance system, not as an ALS type, and it sits at the threshold rather than in the approach area.
- PAPI: a vertical glide-path indicator beside the runway. It is neither an ALS nor runway lighting (FAA no longer installs VASI as a new facility).
FAA Order JO 6850.2C is the installation-criteria document for ALSF-2/SSALR, MALS, MALSF, MALSR and ODALS, and for REIL and PAPI. AC 150/5340-30J, Chapter 7 ("Economy Approach Aids") covers MALSF/MALS, ODALS, REIL and PAPI.
Common Runway Lighting Systems
Runway Edge Lighting
- LIRL, Low-Intensity Runway Lights: visual runways at small airports; one brightness step
- MIRL, Medium-Intensity Runway Lights: visual and non-precision instrument runways; three steps
- HIRL, High-Intensity Runway Lights: precision instrument runways; five steps
Edge lights are white. On MIRL and HIRL instrument runway ends, the last 2,000 ft (610 m) of the runway, or half its length if that is less, shows yellow toward the instrument approach as a caution zone during rollout.
Other Runway Lighting
- Threshold lights: green to arriving aircraft, red toward the runway end
- Runway-end lights: red
- Runway centreline lights: 50 ft (15 m) spacing; white, then alternating red and white from 3,000 ft to 1,000 ft remaining, then all red for the last 1,000 ft
- Touchdown-zone lights: two rows of transverse three-light bars from 100 ft to 3,000 ft, or to mid-runway on shorter runways
- Stopway lights: red, where a stopway exists
Not runway lighting: runway guard lights, stop bars and clearance bars belong to taxiway and hold-position lighting (AC 150/5340-30J, Chapter 4). They protect the runway but are neither ALS nor runway lighting.
A Simplified Airport Lighting Arrangement
The ALS is outside the runway and begins at the landing threshold. The runway lighting is associated with the runway itself. The two meet at the threshold.
Function-by-Function Comparison
| Function | ALS | Runway Lighting |
|---|---|---|
| Locate the runway | Yes, from a distance | Yes, at closer range |
| Establish approach alignment | Yes (primary function) | Limited |
| Roll, height and distance cues on approach | Yes | Limited |
| Vertical glide-path guidance | No. PAPI (or the ILS) provides this | No. PAPI (or the ILS) provides this |
| Identify runway edges | No | Yes |
| Identify threshold | Yes: green threshold bar within the ALS | Yes: threshold lights |
| Centreline guidance | Approach centreline (outside the runway) | Runway centreline (selected runways) |
| Touchdown guidance | No | Yes, where touchdown-zone lights are installed |
| Rollout guidance | No | Yes: edge lights, plus centreline lights where installed |
| Take-off guidance | No | Yes |
Approach Centreline vs Runway Centreline
This is an important distinction.
Approach Centreline
Located outside the runway, on the extended centreline, starting at the threshold. Its purpose is to extend the runway direction visually into the approach area. ALSF-2 centreline bars sit on 100 ft stations; MALS/MALSR bars on 200 ft stations.
Runway Centreline
Located on the runway at 50 ft (15 m) spacing. Its purpose is lateral guidance during landing, rollout and take-off. It is required on CAT II/III runways, on CAT I runways used for landing below 2,400 ft (750 m) RVR, and on runways used for take-off below 1,600 ft (480 m) RVR unless FAA approves otherwise.
Approach centreline ≠ runway centreline. They work together but serve different phases of flight.
Intensity Classification
Approach Lighting
- ALSF-2 → High (5 steady-burning steps, 3 flasher steps)
- ALSF-1 → High (legacy)
- MALSR → Medium (3 steps)
- MALSF → Medium (3 steps)
- MALS → Medium (3 steps)
Runway Edge Lighting
- LIRL → Low (1 step)
- MIRL → Medium (3 steps)
- HIRL → High (5 steps)
The words "medium" and "high" must therefore be read within each system's own classification. A medium-intensity ALS does not imply MIRL, and a high-intensity ALS does not imply HIRL.
Electrical Engineering Comparison
Series-fed airfield lighting follows one familiar chain, and much of the runway system uses it. The ALS does not always follow it.
Constant Current Regulator (CCR) → Primary series circuit → Isolation transformers → Light fixtures.
Approach Lighting
- ALSF-2: 6.6 A or 20 A series circuits with isolation transformers (20 A units are typical), plus sequenced-flasher equipment and control cabinets
- MALS / MALSF / MALSR: steady-burning lights typically fed from a 120/240 V constant-voltage supply (FAA MALS and MALSR use 120 V lamps), not from a CCR loop
- Flashers: discharge-type flashing light units
- Monitoring and remote-control interface (ALCMS where fitted)
Runway Lighting
- HIRL / MIRL: series circuits with CCRs and isolation transformers are recommended; base-mounted fixtures must be on series circuits
- LIRL: parallel circuits (120/240 V) are recommended; stake-mounted MIRL may also use parallel
- Centreline and touchdown-zone lights: 6.6 A series circuit up to 30 kW total load, 20 A above that, with isolation transformers
- Runway control and monitoring (ALCMS where fitted)
Isolation transformers are L-830 for 60 Hz systems and L-831 for 50 Hz systems, so 50 Hz networks such as India's need the L-831 type. Confirm circuit type, load and monitoring against FAA Order JO 6850.2C (ALS) and AC 150/5340-30J (runway lighting and economy aids) before design.
Control System Comparison
ALS Control
- Remote control is required for every FAA ALS (landline or radio; landline only for ALSF-2)
- Sequenced flashers may run only while the steady-burning lights are on
- ALSF-2: five steady-burning steps, three flasher intensities
- MALSR: RAIL can be switched separately; pilots can key the radio 7, 5 or 3 times for high, medium or low, with a 15-minute timer
- Monitoring is required on all steps for ALSF-2 (CAT II/III) and not required for CAT I systems
FAA practice controls MALSR separately from the runway edge lights. Where a runway has both an ALS and runway lighting, air-to-ground radio control of the ALS takes precedence and the runway lights sit at a preset intensity.
Runway Lighting Control
- Edge-light intensity: 1 step (LIRL), 3 steps (MIRL), 5 steps (HIRL)
- Centreline lights controlled independently of touchdown-zone lights and HIRL
- Local control by switch, photocell or timer; remote control from the tower or by radio
- Edge lighting that supports CAT II/III should be remotely monitored, with status reported to the tower
REIL, where installed, can follow the runway edge-light circuit intensity.
What the Pilot Sees
During Approach
Approach lights → Threshold → Runway. The ALS helps answer: "Can I visually acquire and align with the runway?"
During Landing
Threshold → Runway edge, runway centreline, touchdown zone. The runway lighting helps answer: "Where is the usable runway surface and where should I maintain alignment?"
ALS + Runway Lighting Work Together
They are not competing systems. They form one continuous visual guidance chain:
Instrument approach → Approach lighting → Threshold → Runway lighting → Touchdown → Rollout.
Where the two systems meet
- Both place green threshold lights at the landing threshold, 2 to 10 ft before it.
- With a displaced threshold that has runway centreline lights, the controls are interlocked. If a medium-intensity ALS is installed in the displaced area, the displaced-area centreline lights must be off whenever the ALS is on. A high-intensity ALS washes out those lights, so separate circuiting is not required.
CAT I Runway Example
Approach Side
MALSR (or another CAT I ALS such as ALSF-2 operating in SSALR mode) → Threshold.
Runway
HIRL and threshold/end lights on the precision runway. Centreline and touchdown-zone lights are added where landing below 2,400 ft (750 m) RVR is authorised. Centreline lights are also recommended on CAT I runways wider than 170 ft (50 m) or used by aircraft with approach speeds above 140 kt.
The ALS helps with approach and runway acquisition. The runway lighting supports landing and rollout. Runway visual range (RVR) minima decide which optional runway lights are needed.
CAT II/III Runway Example
Approach
ALSF-2 → Threshold. FAA treats ALSF-2 as the high-intensity system for CAT II and III approaches.
Runway
HIRL, runway centreline lights and touchdown-zone lights, all required for CAT II/III, with edge lighting remotely monitored to the tower.
The combination provides extensive visual information during low-visibility operations. Low-visibility taxi lighting (taxiway centreline lights, stop bars) belongs to a separate system and is not covered here.
Main Engineering Difference
| Engineering Area | ALS | Runway Lighting |
|---|---|---|
| Design reference | Approach light plane at threshold elevation, kept clear of obstructions | Runway geometry: edge line 2 to 10 ft from the pavement edge, spacing no more than 200 ft |
| Primary reference point | Landing threshold and extended centreline | Runway centreline and edges |
| Installation area | Approach zone; light plane 400 ft wide. Land needed: ALSF-2 2,600 × 400 ft; MALSR 1,600 × 400 ft plus 1,000 × 25 ft for RAIL | Runway pavement edges, threshold, end and centreline |
| Mounting | Frangible structures up to 6 ft, low-impact-resistant structures 6 to 40 ft, semi-flush lights in paved areas | Elevated (base or stake mounted) edge lights; in-pavement centreline and touchdown-zone fixtures |
| Light alignment | Aimed into the approach with station-specific vertical angles; beams parallel to the extended centreline | Edge lights toed in per manufacturer; touchdown-zone lights toed 4° toward the centreline |
| Main visual purpose | Approach acquisition | Landing and take-off guidance |
| Flashing controls | Sequenced flashers toward the threshold, twice per second, on ALSF-2, MALSF, MALSR and SSALR | None (REIL is a separate synchronised-flash aid) |
| Red lights | ALSF-2 side-row bars in the inner 900 ft | Runway-end lights, red half of threshold lights, red centreline lights in the last 1,000 ft, stopway lights |
| Threshold lights | Green threshold bar, 2 to 10 ft before the threshold | Threshold and end lights, 2 to 10 ft before the threshold |
| Centreline | Approach centreline bars at 100 ft (ALSF-2) or 200 ft (MALS/MALSR) stations | Runway centreline lights at 50 ft spacing |
| Touchdown zone | No | Yes, where required |
Myths vs Facts
They are different visual-aid systems in different areas, installed to different FAA criteria and operated with separate controls.
No. An ALS provides approach guidance; runway lighting provides runway guidance.
An ALS gives alignment, roll, height and distance cues. Vertical guidance comes from the ILS glide slope and, visually, from PAPI.
Whether an ALS is provided, and which type, depends on the approach procedure, visibility minima and operational need. Many visual runways have none.
The two systems have separate classifications, brightness steps and controls. FAA practice controls MALSR separately from the runway edge lights.
ALSF-2 uses series circuits, but MALS, MALSF and MALSR are typically fed from a 120/240 V constant-voltage supply. Always check the circuit type for the specific system.
Memory Diagram
Remember: ALS = before the runway, ending at the threshold. Runway lighting = on the runway.
Engineering Verdict
Approach Lighting System: Provides visual guidance from the approach to the runway threshold. Examples: ALSF-2, MALSR, MALSF, SSALR (legacy or no longer installed new: ALSF-1, MALS, ODALS).
Runway Lighting System: Defines the usable runway and guides the pilot on it. Examples: LIRL, MIRL, HIRL, threshold and end lights, runway centreline lights, touchdown-zone lights.
Engineering & Expert Notes
Keep Their Roles Separate in Design and Maintenance
ConceptThe approach system helps acquisition and alignment; runway lighting supports landing and roll. Faults in each affect different phases.
Separate Circuits Help Isolation
ElectricalDistinct circuits allow one part to be worked on without taking down the other. Check the segmentation.
Inspect Both at Night From the Pilot's View
InspectionWalking the pattern in darkness shows gaps and dim units that daytime checks miss.
Coordinate Outages and NOTAMs
OperationsA problem in either system may affect operations. Plan work and notices together.
Frequently Asked Questions
No. An ALS starts at the landing threshold and extends outward into the approach area, while runway lighting is installed on or along the runway itself. They are separate but complementary systems with separate FAA installation criteria and separate controls.
No. Whether an ALS is provided, and which type, depends on the approach procedure, the visibility minima and the operational need. Visual runways commonly have none, and CAT II/III operations call for ALSF-2.
No. The approach centreline extends the runway direction into the approach area outside the runway, while the runway centreline lights provide lateral guidance on the runway itself.
Not directly. Approach lighting and runway edge lighting use separate intensity classifications and separate brightness steps, so each term must be read within its own system.
Runway lighting, particularly touchdown-zone lights where installed, provides the visual reference for touchdown and rollout. The approach lighting system does not.
Not in the way PAPI does. An ALS gives alignment, roll, height and distance cues. Vertical guidance comes from the ILS glide slope and, visually, from a PAPI beside the runway.
Those are FAA names. Indian aerodromes follow ICAO Annex 14 as implemented in DGCA CAR Section 4, Series B, Part I, which describes approach lighting by function (simple, precision CAT I, precision CAT II/III) rather than by FAA acronym. See section 22 for the main differences.
FAA vs ICAO / DGCA: Where the Details Differ
The ALS-versus-runway-lighting concept is the same everywhere. Names, dimensions and colour coding differ, so do not carry FAA numbers into an ICAO or DGCA project. Values below are for orientation only; verify them against the current edition of Annex 14 and the DGCA CAR.
| Item | FAA (this page) | ICAO Annex 14 / DGCA |
|---|---|---|
| Approach lighting names | ALSF-2, MALSR, MALSF, MALS, ODALS | Simple approach lighting; precision approach CAT I lighting; precision approach CAT II/III lighting |
| Typical length | 2,400 to 3,000 ft (precision); 1,400 ft (non-precision) | 900 m for precision CAT I and CAT II/III; at least 420 m for simple approach lighting, where practicable |
| Runway centreline colour coding | Alternating red/white from 3,000 ft to 1,000 ft remaining; red in the last 1,000 ft | Alternating red/white from 900 m to 300 m remaining; red in the last 300 m |
| Yellow edge-light zone | Last 2,000 ft (610 m) or half the runway, whichever is less | Last 600 m or one-third of the runway, whichever is less |
| Governing documents | FAA Order JO 6850.2C; AC 150/5340-30J | ICAO Annex 14 Vol. I; ICAO Doc 9157 Part 4; DGCA CAR Section 4, Series B, Part I |
Governing Documents
This page is educational. For an actual project, confirm the current revision of each document and follow the approved project specification and drawings.
FAA Order JO 6850.2C
Visual Guidance Lighting Systems (30 Aug 2022). Installation criteria for ALSF-2/SSALR, MALS, MALSF, MALSR, ODALS, REIL and PAPI.
FAA AC 150/5340-30J
Design and Installation Details for Airport Visual Aids (12 Feb 2018). Runway and taxiway edge lighting, runway centreline and touchdown-zone lighting, taxiway lighting and economy approach aids. Mandatory for AIP- and PFC-funded projects; check faa.gov for a newer revision.
FAA AIM, Chapter 2, Section 1
Pilot-facing description of approach lights, REIL, runway edge, centreline and touchdown-zone lights.
FAA Equipment Specifications
AC 150/5345-46 (light fixtures), AC 150/5345-10 (CCRs), AC 150/5345-47 (isolation transformers), AC 150/5345-56 (ALCMS) and AC 150/5340-26 (maintenance of visual aids).
ICAO and DGCA
ICAO Annex 14 Volume I, ICAO Aerodrome Design Manual (Doc 9157) Part 4, and DGCA CAR Section 4, Series B, Part I (Aerodrome Design and Operations) for Indian aerodromes.
Final Engineering Note
Approach lighting and runway lighting are separate systems that work together as one continuous visual guidance chain. Verify the exact configuration, circuit type and brightness steps against the current applicable standard and the approved project drawings.
Approach lighting helps the pilot find and align with the runway; runway lighting helps the pilot land, roll and operate on the runway.
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