Aeronautical & General Instruments Limited Fleets Point | Willis Way | Poole | Dorset | BH15 3SS | UK T +44(0) 1202 685661 F +44(0) 1202 685670 E [email protected] W agiltd.co.uk AGIVIS CAT III FSM Forward Scatter IRVR System Technical Description

Introduction Runway Visual Range (RVR) is defined by the International Civil Aviation Organisation (ICAO) as: “The distance over which the pilot of an aircraft on the centreline of a runway can see the runway surface markings or the lights delineating the runway or identifying its centre line.” Because it is not possible to measure RVR directly, an assessment is made, either by a human observer or using an automated system to provide what is called Instrumented Runway Visual Range, (IRVR). The reliable and accurate assessment of RVR is essential if airport operations are to run as safely and...

Principle of Operation The most important factor in assessing RVR is to establish the atmospheric extinction coefficient or the related value for atmospheric transmittance. The extinction coefficient represents the attenuation of light passing through air due to two effects:  The scattering of light by airborne particles The absorption of light by airborne particles Forward scatter based IRVR systems can detect extinction due to the scattering of light caused by both suspended (solid) and precipitating (water) particles. The amount of scattering is related to the quantity of particles in the...

To ensure repeatability of measurements between individual instruments, the ICAO specifies that the calibration of forward scatter sensors must be traceable and verifiable to a transmissometer comparison. This is true for the Biral sensors used for AGIVIS FSM. Biral VPF-730 Sensor Head Product Brochure can be found at: http://www.biral.com/wp-content/uploads/2014/09/DS-730DOC101255.02A.pdf Every 60 seconds the system determines a value for extinction coefficient and uses it to perform calculations according to two different equations:  Koschmieder’s Law is a method of assessing visibility based...

IRVR calculations are usually carried out using a rolling 10 minute mean of extinction coefficient. However, the system is capable of recognising what is called a ‘marked discontinuity’ in visibility. This is defined by the WMO as: “…an abrupt and sustained change in runway visual range, lasting at least 2 minutes, which reaches or passes through criteria for the issuance of SPECI reports…” If a marked continuity is detected the system automatically uses only IRVR values occurring after the discontinuity occurred. Field Site Equipment The number of field sites depends on the requirements and...

Rack Equipment IRVR data from each field site is reported to other system equipment, usually mounted in a 19” rack positioned in the ATC tower’s equipment room. The necessary data links can be copper, fibre optic or wireless. The receiving modems and other system inputs are all contained in the tower equipment rack. Field site IRVR data is fed to the disseminator, which acts as the central data processor and communication node for the system. The disseminator synchronises to the ATC system clock and also has an internal clock as a back-up. It also receives the runway light intensity and runway...

The system also includes a local RVR display, master alarm light and external alarm relay outputs. AGIVIS Rack Assembly Users may interface to the disseminator via the keyboard and video display unit. This interface displays live system status along with diagnostic and maintenance information. Raw sensor data may be viewed as well as system archives, and commands sent direct to field sites. System configuration can also be reviewed and updated. IRVR, alarm and system status information can all be supplied for integration to Automated Weather Observing System (AWOS) or other Met and ATC systems....

The displays can trigger visual and audible alarms when fog or Low Visibility Procedures (LVP) thresholds are crossed. IRVR Display Layout Standards AGIVIS FSM complies with all relevant international standards, including:      ICAO Annex 3 (Meteorological Service for International Air Navigation) ICAO Manual on Automatic Meteorological Observing Systems at Aerodromes (Doc 9837) ICAO Manual of Aeronautical Meteorological Practice (Doc 8896) ICAO Manual of Runway Visual Range Observing and Reporting Practices (Doc 9328) WMO CIMO Guide The system also complies with a number of national standards...

Specifications AGIVIS FSM System Measurement Range Light Source Near Infra-Red Field Sites Operating Temperature Relative Humidity Power Requirements Environmental Protection Rack Equipment Operating Temperature Relative Humidity Power Requirements IRVR Displays Operating Temperature Relative Humidity Power Requirements -10°C to +40°C 95% non-condensing 12V DC (an in-line 90V to 264V, 50Hz to 60Hz AC PSU can be supplied) Contrast Ratio AGI is dedicated to the continuous improvement of its products. If specific requirements exist that are not covered by this Technical Description, we are always...