The Significance of Airport Runway Markings: CAT I and CAT II for Safe Landings

During my recent visit to the airport, I noticed an intriguing sign on the runway. The sign indicated the Category I (Cat I) and Category II (Cat II) landing categories, which are crucial for ensuring safe landings under different visibility conditions. These categories provide essential information to pilots about the precision and visibility required for a safe landing, especially in adverse weather conditions.

Understanding Category I (Cat I) and Category II (Cat II) Landings

Category I (Cat I) allows for a minimum visibility of 550 meters (about 1,800 feet) with a decision height of 200 feet above the runway. The term decision height refers to the altitude at which a pilot must decide whether to continue with the landing or to initiate a go-around. If the runway is not visible or otherwise determined to be unsafe below this height, the landing attempt must be aborted to ensure safety.

Category II (Cat II) provides for lower visibility requirements, typically allowing for a decision height as low as 100 feet and visibility as low as 350 meters (about 1,150 feet). This category is designed for situations where pilots need to rely on instrument approaches rather than visual references.

Both categories are rated based on RVR - Runway Visual Range and DH - Decision Height. These measures are critical for pilots to understand the visibility and decision-making requirements for safe landings.

Placement of Stop Signs for CAT I and CAT II

These categories not only help in determining the visibility and decision height but also inform pilots about where to stop before the runway. The farther the CAT level (e.g., CAT 2 or CAT 3), the farther pilots must stop from the runway. This is especially important in foggy or low-visibility conditions, where the runway may not be clearly visible. The appropriate position is critical for pilots to ensure they can safely see the runway and make a decision above the required DH.

The Role of Instrument Landing Systems (ILS) and Visibility

All of this is closely related to the Instrument Landing System (ILS) and visibility conditions, particularly during foggy or cloudy weather. ILS is an essential piece of equipment that enables pilots to land safely, even when visibility is poor. The use of ILS allows pilots to rely on instrument references rather than visual ones, ensuring safe landings in adverse conditions.

In the U.S., an ILS can have CAT I visibility minimums as low as 0.75 miles with a runway visual range of 4,000 feet if there are no obstructions on the required obstacle clearance surfaces. Lower visibility conditions of 0.5 miles with a runway visual range of 2,400 feet are also possible if a high-intensity approach light system (ALS) is available. The ALS significantly extends the runway environment towards the landing aircraft, allowing for low-visibility operations.

Complexity of ILS and Visibility Requirements in Different Categories

For CAT II and III ILS approaches, more complex high-intensity approach light systems are usually required. Medium-intensity systems are typically paired with CAT I ILS approaches. At many non-towered airports, control of the lighting system is left to the pilot. They can use radio signals to control the intensity of the lights: 7 clicks for high intensity, 5 clicks for medium intensity, and 3 clicks for low intensity.

Conclusion

Proper understanding and adherence to airport runway markings and procedures based on Category I and II landings are vital for ensuring the safety of aircraft during approach and landing. These procedures, in conjunction with the use of ILS and appropriate lighting systems, are crucial in maintaining safe operations, especially under low-visibility conditions.