What Are Category I (CAT I) Runways?

This is the third instalment in our set of articles on different runways and their requirements.

Category I (CAT I) Instrument Flight Rules are precision approach runways as defined by FAA and ICAO.

Precision Instrument Flight Rules (CAT I) is an operation of precision instrument approach and landing based on the Decision Height (DH) and the Runway Visual Range (RVR). CAT I operations rely on altimeter indications, vertical & lateral guidance, and waypoints to assist pilots in conducting an approach to land without visual reference to the ground. CAT I is a subsection of IFR, which you can read more about in our previous article.

Decision Height (DH) is the lowest height or altitude in the approach descent. The pilot must initiate a missed approach if the required visual reference to continue the approach is not visible to the pilot.

The visual references include:

• The threshold
• The threshold markings
• The threshold lights
• The runway end identifier lights
• The visual glideslope indicator
• The touchdown zone or touchdown zone markings
• The touchdown zone lights
• The runway or runway markings
• The runway lights

The minimum decision height for Category I operations is 60 metres (200 feet) for both ICAO and FAA.

Runway Visual Range (RVR) is the distance over which a pilot of an aircraft on the runway’s centreline would see the runway surface markings or lights delineating the runway or identifying its centre line. The Runway Visual Range (RVR) for Category I operations are between 550 metres (1800 feet) and 800 metres (2600 feet) for ICAO and FAA, depending on the conditions of the approach and equipment.

Precision instrument approach operations must have non-visual, vertical guidance information (glide slope or WAAS) displayed to the pilot; without vertical guidance information displayed in the cockpit, the operation is considered non-precision.

What are the lighting requirements on a CAT I runway?

There are different rules and regulations for ICAO and FAA CAT I Precision Instrument runways.

High-intensity runway lights are required for CAT I operations. Fixtures are positioned along the runway edges emitting white light, except in the caution zone, which is the last 610m or 200 feet of the runway or half the runway length (whichever is less). In the caution zone, the fixtures emit white light in the direction facing the runway threshold and yellow light in the opposite direction.

Runway threshold or end lighting is a prerequisite. It is to be positioned at either end of a runway. They consist of at least six fixtures for ICAO specification or eight fixtures for FAA specification equally spaced not more than three metres from the runway extremity.

Bi-directional red/green lighting must be used if the airfield is used in both directions. When a runway is used in both directions, bi-directional red/green lighting is required. Taxiway Lighting must be positioned along the edges of each taxiway, emitting blue light to define its lateral limits. The same rules apply to the location and colour output as VFR and IFR runways.

Runway Edge Identification Lighting (i.e., REILs) should be installed at the threshold of a precision approach runway in most circumstances. They provide rapid and positive identification of the approach end of a particular runway. The system consists of a pair of synchronised flashing lights.

Both ICAO and FAA require Precision Approach Path Indicators (PAPIs) to conduct IFR CATI operations. PAPIs provide a visual aid for guidance information to help a pilot acquire and maintain the particular runway’s correct approach. This is usually 3 degrees from horizontal.

An approach lighting system must be implemented to provide visual guidance for circling, offset, and straight-line approaches. This helps lower visibility minimums, allowing pilots to identify their location on the approach and depends on the type of approach lighting system installed. The approach lighting system can be in the form of a MALSR, SSALR or ALSF configuration depending on the operational and environmental needs of the individual site and regional airport guidelines.

Airfield Rules Series

1. What Is a Visual Flight Rules (VFR) Airfield?
2. What Is an Instrument Flight Rules (IFR) Airport?
3. What Are Category I (CAT I) runways?