"How is RVR measured and reported?"

"RVR is measured using automated sensors (transmissometers or forward scatter sensors) that quantify atmospheric clarity (MOR), ambient light, and runway lighting intensity. The data is processed using ICAO algorithms to provide RVR values at key runway locations (touchdown, midpoint, rollout), updated typically every minute."

"When is RVR reporting required at airports?"

"RVR reporting is mandatory whenever prevailing visibility drops below 1,500 meters (5,000 feet), and is essential below 800 meters (2,600 feet) or during precision instrument approaches. Accurate RVR values are central to issuing takeoff and landing clearances and activating low-visibility procedures."

"Why is RVR important for flight operations?"

"RVR directly determines whether a runway can be used for takeoff or landing under instrument flight rules, especially for Category I, II, and III approaches. It helps pilots, air traffic controllers, and airport operators maintain safety and comply with regulatory minima during adverse weather."

"What technologies are used to measure RVR?"

"Modern RVR systems use transmissometers or forward scatter sensors to measure Meteorological Optical Range (MOR), along with ambient light meters and runway light intensity monitors. These inputs are processed with ICAO-approved algorithms to calculate RVR in real time."

Runway Visual Range (RVR)

Q: "What is Runway Visual Range (RVR)?"

"RVR is the distance over which a pilot on the runway centerline can see and identify runway markings or lights, measured in meters or feet. It is the primary visibility metric for safe takeoff and landing under low-visibility conditions, tailored to the operational environment of the runway."

RVR (Runway Visual Range) quantifies how far a pilot can see runway markings or lights from the runway centerline, essential for safe low-visibility operations.

Aviation Meteorology Runway Safety Airport Operations

Runway Visual Range (RVR) in Meteorology

What is Runway Visual Range (RVR)?

Runway Visual Range (RVR) is a specialized measurement in aviation meteorology, defined as the distance along a runway over which a pilot, positioned on the runway centerline, can see and identify runway surface markings or the lights marking the centerline or edges. RVR is not simply a measurement of atmospheric visibility; it is a calibrated, operational metric that specifically addresses what a pilot can actually see from the cockpit under current weather and lighting conditions.

RVR is reported in meters (or feet) and is the key reference for safe aircraft operations during takeoff and landing, especially under low-visibility conditions such as fog, heavy precipitation, or darkness. Its value ensures that pilots and air traffic controllers have a standardized, objective basis for making critical operational decisions.

Regulatory Framework and Importance

RVR is governed by international and national aviation standards, including ICAO Annex 3, ICAO Doc 9328, FAA orders, and EASA regulations. It serves as the controlling visibility parameter for precision instrument approach and landing operations—particularly for runways equipped with Instrument Landing Systems (ILS) or other advanced navigation aids.

Minimum RVR values are strictly defined for each approach category:

Category	Decision Height (DH)	Minimum RVR	Use Case
CAT I	200 ft	550 m (1,800 ft)	Standard ILS approaches
CAT II	100 ft	300-350 m (1,200 ft)	Enhanced ILS, advanced lighting
CAT IIIa	<100 ft or none	≥200 m (700 ft)	Very low visibility, advanced aircraft
CAT IIIb	<50 ft or none	50–200 m (150–700 ft)	Lowest visibility, special certification
CAT IIIc	None	No RVR limit	Zero visibility (not operationally used)

RVR is mandatory for reporting and operational compliance whenever visibility drops below 1,500 meters (5,000 feet), and is vital below 800 meters (2,600 feet) or during any precision approach.

RVR vs. General Visibility

Whereas general (surface) visibility describes how far a stationary observer can see an object of known size and contrast, RVR focuses on the pilot’s perspective from the runway, factoring in:

The brightness and configuration of runway lights
Markings visible from the cockpit
Background luminance (ambient light)
Atmospheric clarity (fog, precipitation, dust, etc.)

As such, RVR can differ significantly from general visibility, especially at night or in rapidly changing weather.

Measurement Methods

Manual Assessment

Historically, RVR was assessed by trained observers who counted the number of runway lights visible from a fixed location, then referred to tables to estimate visibility. While still used as a backup, this method is subjective and less accurate, especially in rapidly changing or hazardous conditions.

Automated RVR Systems

Modern airports use automated systems comprising:

Transmissometers: Two-mast systems measuring the direct attenuation of light over a fixed distance (the gold standard for RVR).
Forward Scatter Sensors: Single-mast systems that infer visibility by measuring the scattering of light by atmospheric particles.
Ambient Light Sensors: Quantify background luminance, vital for accurate perception modeling.
Runway Light Intensity Monitors: Ensure actual lighting levels are factored into the calculation.

These systems are placed at key runway locations—touchdown zone (TDZ), midpoint (MID), and rollout/stop end (END)—to provide real-time, zone-specific visibility readings.

Measurement Concepts

Meteorological Optical Range (MOR): Fundamental input, representing the distance at which a beam of light is attenuated to 5% of its original intensity.
Background Luminance: The brightness of the environment, affecting the contrast and visibility of runway lights.
Runway Light Intensity: The measured output of edge, centerline, or touchdown zone lights.

Algorithmic Calculation

RVR is calculated using Allard’s Law and Koschmeider’s Law, which combine the measured MOR, light intensity, and background luminance with pilot visual thresholds to determine the maximum distance at which runway lights or markings remain discernible.

Operational Application

Air Traffic Control and Pilots

RVR guides pilots and ATC in deciding whether it’s safe to use a runway for takeoff or landing, especially under instrument flight conditions. Each approach category has a minimum required RVR; operations below this value are prohibited unless both aircraft and crew are specially certified.

Airport Capacity

As RVR decreases, airport capacity drops. Lower RVR values trigger reduced landing and takeoff rates, stricter ground movement controls, and the activation of low-visibility procedures (LVPs) to maintain safety.

RVR State	RVR Range	Max Landings/hr
State 1	>1000 m	22
State 2	1000–550 m	18
State 3	550–300 m	13
State 4	<300 m	10

Real-World Scenarios

Dense Fog: If RVR falls to 175 meters at touchdown and lower at rollout, only CAT IIIb certified operations are allowed; all others are suspended.
Sudden Visibility Drop: ATC notifies inbound flights and may suspend approaches or initiate diversions when RVR falls below published minima.
Capacity Management: Accurate RVR measurement has enabled some airports to safely increase landings during fog compared to conservative estimates, reducing delays and diversions.

Technical Standards and Compliance

ICAO Doc 9328: Defines RVR observing and reporting procedures.
ICAO Annex 3: Sets meteorological service standards.
FAA-E-2772B: US standards for RVR system performance and reporting.
WMO No. 8: Meteorological instrumentation guidance.
CAP 746 (UK): UK CAA standards for RVR.

Equipment must be certified and maintained to these standards, including regular calibration and sensor checks.

Summary

RVR is a critical, regulated component of aviation safety and operational efficiency. It provides pilots and controllers with a precise, actionable measure of runway visibility, tailored to the cockpit perspective and actual runway environment. Modern automated RVR systems, governed by rigorous international standards, ensure the safe and efficient movement of aircraft in all weather conditions.

Frequently Asked Questions

What is Runway Visual Range (RVR)?: RVR is the distance over which a pilot on the runway centerline can see and identify runway markings or lights, measured in meters or feet. It is the primary visibility metric for safe takeoff and landing under low-visibility conditions, tailored to the operational environment of the runway.
How is RVR measured and reported?: RVR is measured using automated sensors (transmissometers or forward scatter sensors) that quantify atmospheric clarity (MOR), ambient light, and runway lighting intensity. The data is processed using ICAO algorithms to provide RVR values at key runway locations (touchdown, midpoint, rollout), updated typically every minute.
When is RVR reporting required at airports?: RVR reporting is mandatory whenever prevailing visibility drops below 1,500 meters (5,000 feet), and is essential below 800 meters (2,600 feet) or during precision instrument approaches. Accurate RVR values are central to issuing takeoff and landing clearances and activating low-visibility procedures.
Why is RVR important for flight operations?: RVR directly determines whether a runway can be used for takeoff or landing under instrument flight rules, especially for Category I, II, and III approaches. It helps pilots, air traffic controllers, and airport operators maintain safety and comply with regulatory minima during adverse weather.
What technologies are used to measure RVR?: Modern RVR systems use transmissometers or forward scatter sensors to measure Meteorological Optical Range (MOR), along with ambient light meters and runway light intensity monitors. These inputs are processed with ICAO-approved algorithms to calculate RVR in real time.

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