How CAT IIIB and DGCA Rules Challenge India's Airlines During Winter Fog

The winter season brings radiation fog to northern India. This dense, persistent fog creates extremely low visibility conditions. Compounding this is smog, which makes the fog denser and last longer.

Low Visibility Operations and CAT IIIB Technology

When visibility drops, airports implement Low Visibility Procedures (LVP). This allows for specialized operations like Low Visibility Take-Off (LVTO). The critical technology is the Instrument Landing System (ILS). ILS provides precise guidance for aircraft landings.

CAT IIIB, an advanced ILS category, is essential. It permits aircraft to land when visibility is as low as 50 meters. Not all Indian airports are equipped for this level of operation. India's largest hub, Delhi Airport, is a key exception.

To manage the season, the Directorate General of Civil Aviation (DGCA) sets an official fog window. For the current season, this period is December 10 to February 10. Airlines must deploy CAT IIIB-certified aircraft and trained crew.

Operational Bottlenecks at Major Hubs

Even with advanced technology, disruptions are unavoidable. LVP significantly increases the time between aircraft movements. This ensures safety but creates backlogs and congestion.

For example, Delhi Airport's capacity drops notably during LVP. Normal operations handle about 100 movements per hour. This capacity falls to roughly 65 movements per hour. The airport needs two to three hours to recover from just one hour of fog disruption.

Another challenge is the visibility difference between landing and take-off. CAT IIIB landings can occur at 50 meters visibility. However, take-offs require a minimum of 75 meters visibility. This disparity can quickly congest parking stands. Arriving aircraft land while departing aircraft remain stuck. This congestion often leads to flight diversions. Airlines plan for fair-weather alternative airports, like Ahmedabad.

The Cascading Impact on Airline Networks

Disruptions at major hubs, such as Delhi, have a cascading impact airline networks nationwide. Airlines like IndiGo and Air India use complex flight and crew rotations. A single delay quickly compounds throughout the day.

This problem is severely compounded by the Flight Duty Time Limitation (FDTL) rules. The DGCA has recently tightened these pilot fatigue norms. FDTL rules cap duty and flight time for safety. Time spent waiting for take-off or a gate counts toward the limit. This means pilots can exceed their maximum duty time without flying.

Recent FDTL enforcement exposed crew shortages across the industry. In December 2025, IndiGo faced massive cancellations and delays. The airline had to cut its schedule to comply with the rules. The DGCA issued temporary relaxations for IndiGo until February 2026. This shows the difficulty of balancing safety and operations. Airlines must now hire more pilots and optimize crew rostering. The challenge is particularly acute for carriers with high aircraft utilization.

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Railways' Mitigation Efforts

Fog also severely impacts the Indian Railways network. Trains can be delayed by over 12 hours. The Railways is deploying fog safety devices (FSD). These GPS-based, handheld systems alert locomotive pilots. The Railways is also implementing the Kavach Automatic Train Protection (ATP) system. Kavach allows pilots to maintain speed in dense fog. It flashes signal information inside the locomotive cabin. This system is currently being deployed on high-density corridors.