How to Design and Maintain a Runway Visual Range System

Weather is the most common cause of air traffic delay in the National Airspace System, accounting for almost 75% of delays and over 20% of general aviation accidents. And low visibility is one of the industry’s most persistent weather challenges. 

Weather events — fog, heavy rain, snow and even sandstorms — can dramatically reduce visibility, transforming routine takeoffs and landings into dangerous scenarios impacting airport operations and safety. For managers and technical teams at busy commercial airports, an effective runway visual range (RVR) system equips pilots and air traffic controllers with accurate, real-time visibility data to inform smarter decision-making.

Understanding Runway Visual Range

Visibility can be understood differently depending on the context it is used in and is often referred to as human observation. The International Civil Aviation Organization defines visibility for aeronautical purposes, while the World Meteorological Organization provides a scientific measure of atmospheric visibility: meteorological optical range, or MOR. With an aviation-specific purpose and definition, RVR precisely measures the distance a pilot can see along a runway with runway lights and markings — and can be up to five times greater than MOR at night. 

Precise RVR assessments become mandatory when visibility dips below 800 meters, according to the ICAO. Below 800 m visibility, RVR reporting is mandatory for precise approaches and landings. The RVR reporting range is from below 50 m to 2000 m. RVR values are reported along the runway, representative of touchdown, midpoint and endpoint zones. RVR averaging is either 10 minutes for METAR and SPECI reports or one minute for operational use, such as local routine and special reports and ATC displays. 

Historically, human observers manually assessed visibility by counting runway edge lights and estimating RVR in meters. Only allowed in Category I instrumented landing systems (ILS) operations, the human observer method remains impractical since a person only collects data at periodic intervals, with human variations potentially introducing errors. 

As airport technology evolved, so did the approach to measuring runway visibility. With more sophisticated automated sensing technologies, how can airports design and maintain this critical safety infrastructure? 

Designing an Effective RVR System

Sensor Technology: The Foundation of Accurate RVR

Modern RVR system assessments rely on three key components: MOR, background luminance and runway lighting. MOR is based on measurements from two primary sensor technologies, each offering distinct advantages for different operational environments:

1.      Transmissometers directly measure light attenuation and have been the gold standard, providing fail-safe, precise readings.

2.      Forward scatter sensors measure light scattering caused by airborne particles, but weather conditions and particle types heavily influence their operational accuracy. Operators often choose these sensors because they require only one mast, making them cheaper to purchase and install than transmissometers.

Consequently, selecting the right technology depends on an airport’s specific operational needs. 

High-traffic or international hubs, especially Category II and III airports, experiencing frequent low-visibility events might prioritize transmissometers, whereas regional airports, typically running CAT I operations, could benefit from forward scatter sensors’ easier integration, lower costs and flexibility across the visibility range. 

With the right technology, the next critical consideration becomes where and how to deploy these advanced sensors. 

Strategic Placement and Configuration

ICAO recommends positioning RVR sensors at three key runway locations:

1.      Touchdown: Provides visibility data where pilots make critical landing decisions.

2.      Midpoint: Assesses runway conditions along the landing path. If the runway is exceptionally long (more than 3,600 meters), ICAO recommends two midpoint sensors.

3.      Endpoint: Ensures complete visibility coverage for departures and landings. 

Placed at a lateral distance of not more than 120 m from the runway centerline and about 300 m along the runway from the threshold, RVR sensors are installed approximately 2.5 m above the runway, representing the pilot’s view from the cockpit. 

Beyond placement, integrating RVR systems with runway lighting and background luminance measurements also helps decision-makers. RVR readings fluctuate based on lighting conditions, so aligning sensor data with ATC requirements improves operational accuracy. 

Yet technology and placement only form part of the equation. An RVR system’s legitimate value lies in communicating critical information effectively to pilots and ATCs. 

Data Accessibility and System Integration

RVR data is only useful if readily accessible to stakeholders. ATC personnel require real-time, one-minute average RVR values displayed on dedicated screens to relay valuable landing and takeoff information to pilots.

Meteorological platform integration automates consistent visibility data reporting through METAR and SPECI aviation weather reports, streamlining flight planning and air traffic management processes. 

However, sophisticated systems require ongoing care to sustain critical performance standards. 

Maintaining RVR Systems for Long-Term Reliability

Maintenance for Long-Term Reliability

Routine maintenance obviously drives continuous RVR system performance. Best practices include regular sensor and lens cleaning, contamination compensation, automated calibration, and consistent software updates. 

Keeping firmware and processing algorithms up to date optimizes measurement capabilities. ICAO guidelines also emphasize deploying multiple sensors at key runway locations, implementing redundant backup computing units and maintaining alternative display systems to prevent operational disruptions during potential system failures. 

To understand the real-world impact of RVR systems, look no further than a technological transformation in Costa Rica. 

RVR Implementation at Juan Santamaría International Airport

In Costa Rica, the tropical climate shifts between dry and rainy seasons, during which high humidity can reduce visibility to as low as 100 m. Previously reliant on human observers during the rainy season, the Directorate General of Civil Aviation, Costa Rica’s civil aviation authority, implemented an automated transmissometer-based system alongside human observers to ameliorate the detriment of low visibility at the country’s biggest airport, Juan Santamaría International.

The Vaisala LT31-based RVR system integration results were remarkable: Continuous real-time data enabled faster air traffic control decisions during inclement weather events, improved flight scheduling helped reduce delays and adaptability to sudden weather changes ultimately enhanced overall airport efficiency. 

In a country where tourism drives the economy, the DGAV must maintain efficient and comfortable air travel while setting new airport efficiency and safety standards via automatic, real-time RVR measurements. 

Seeing the Approach Forward: Why RVR Investment Pays Off

As aviation technology evolves, modern RVR systems deliver the accurate assessments underpinning operational safety and passenger trust. 

By selecting appropriate sensor technologies, optimizing system design and maintaining robust maintenance protocols, airports can minimize disruptions and elevate safety standards. In an industry where visibility drives efficiency and safety, advanced RVR systems give pilots a good idea of what they can expect to see —or not — on their approach.