4.1.1 RVR and Visibility
The ICAO Annex 14 has the following as a definition for
"Instrument Runway - One of the following types of runways intended for operation of aircraft using instrument approach procedures:
a) Non-precision approach runway - An instrument runway served by visual aids and a non-visual aid providing at least directional guidance adequate for a straight-in approach.
b) Precision approach runway, category 1 - An instrument runway served by ILS and/or MLS and visual aids intended for operations with a decision height (DH) not lower than 60m [200ft] and either a visibility of not less than 800m or a runway visual range (RVR) not less than 550m.
c) Precision approach runway, category 2 - An instrument runway served by ILS and/or MLS and visual aids intended for operations with a DH lower than 60m [200ft] but not lower than 30m [100ft] and a RVR not less than 350m.
d) Precision approach runway, category 3 - An instrument runway served by ILS and/or MLS to and along the surface of the runway, and:
A) - intended for operations with a DH lower than 30m [100ft], or no DH
and a RVR not less than 200m
B) - intended for operations with a DH lower than 15m [50ft], or no DH
and a runway visual range less than 200m but not less than 50m.
C) - intended for operations with no DH and no RVR limitations.
APPROACH LIGHTING
4.1 OVERVIEW
The term "approach lighting" includes a variety of systems that are located at the runway end and serve to facilitate runway acquisition and landing. These systems include:
- Runway Identification Lights (RIL)
- ODALS
- MALSR/SSALR
- ALSF-2
- Visual Approach Slope Indicators
Prior to the late 1980s, the Low Intensity Approach Lighting (LIAL) and High Intensity Approach Lighting systems were used at Canadian Airports. The latter came in two forms ... that for Category 1 operations (HIAL-1) and that for Category 2 operations (HIAL-2).
The LIAL consisted of a row of 15 amber/yellow lights spaced at 60m [200ft] spacings for a system length of 900m [3000ft]. This system was similar to the ICAO "Simple Approach Lighting System", but without the cross-bar. The LIAL system was replaced by ODALS.
The HIAL-1 consisted of 217 lights which was similar to the ICAO Precision Approach Category 1 Lighting System with barrette centreline. The HIAL-1 system was replaced by the MALSR/SSALR.
The HIAL-2 was essentially an HAIL-1 with additional red barrettes near the threshold and augmented cross-bars for a total of 271 lights. This system was similar to the ICAO Precision Approach Category 2 Lighting System with barrette centreline. The HIAL-2 was replaced by ALSF-2.
The above changes in standard provided a benefit in that there is a lesser number of light units per system ... thus power consumption ... and also reductions in length. The SSALR and ALSF-2 are 720m [2400ft] long, whereas the previous systems were 900m [3000ft] long.
The story of approach lighting systems can not be completely told without mention of the towers used for mounting. The towers [Millard Towers], used in Canada, were developed in the 1960s to replace wooden poles. At the time, Norm Hall was the person involved with visual aids in the Transport Canada Headquarters office. He had a cottage near Perth, Ontario [some 90km west of Ottawa] and happened to mention the intention to do replacement of wood poles, to his neighbour John Millard who ran a small electrical construction firm. John subsequently proposed a new design of tower that would be both light in weight and frangible to aircraft. This, when frangibility was not yet a significant issue. The result was a design of aluminum tower which is common at Canadian airports.
Runway identification lights were installed to compliment the old LIAL system, so as to provide visual acquisition of the runway end. The equivalent system, used by the FAA, is referred to as Runway End Identification Lights (RIL).
The term Visual Approach Slope Indicator system, as will be further explained in the section on PAPI, is generic as well as specific to a particular type of system. As a generic term, it refers to a number of types of indicator. As a specific term, it refers to the VASI system commonly used at Canadian airports some years ago.
