Why Do Delhi Airport Fog Delays Persist? The CAT IIIB System Explained

Dense winter fog has again severely impacted air travel across North India, with Indira Gandhi International (IGI) Airport in Delhi at the epicenter. The disruption is significant, with reports of 118 flights cancelled and 16 diverted on one morning alone, following a similar pattern the previous day with 128 cancellations. As India’s busiest aviation hub, handling over 1,500 flight movements daily, disruptions at Delhi create cascading delays across the entire national network.

The Core Problem: Visibility and Safety

Fog leads to sharply reduced visibility at airports. This low visibility makes aircraft take-offs and landings more difficult. To ensure safety, air traffic control (ATC) must space out aircraft movements. This necessary slowing creates a massive backlog of scheduled flights. The key measurement here is Runway Visual Range (RVR). RVR is the distance a pilot can see runway markings or lights.

India’s aviation regulator, the Directorate General of Civil Aviation (DGCA), enforces strict rules. The DGCA bars flights from taking off when visibility falls below 125 meters. This rule forces diversions to other airports. Airlines must ensure aircraft carry extra fuel for these potential diversions.

Delhi's Defense: CAT III-B Technology

To counter the North India winter fog, the aviation ecosystem relies on the Instrument Landing System (ILS). ILS is a precise guidance system helping aircraft land in low visibility. The most advanced category is CAT III.

• CAT I: Allows landing with RVRs above 550 meters.
• CAT II: Allows landing with RVRs between 300 and 549 meters.
• CAT III: Allows landing in extremely low or near-zero visibility.

Delhi Airport has four runways. Three of these runways are CAT IIIB compliant at both ends. The fourth runway remains CAT-I compliant. CAT IIIB operations permit landings when RVR is less than 200 meters but not less than 50 meters. This is a significant operational capability. Currently, six Indian airports—Delhi, Lucknow, Jaipur, Amritsar, Bengaluru, and Kolkata—are equipped for CAT IIIB operations. India does not yet have an airport capable of the most advanced CAT IIIC operations, which allow for zero-visibility landings.

Why Disruptions Still Occur

Despite the advanced ILS, flight disruptions persist for several reasons:

• Aircraft and Pilot Compliance: Not all aircraft are equipped with the necessary gear for CAT III landings. Furthermore, not all pilots are trained and certified for DGCA low visibility procedures.
• Crew Duty Time: Delays cause flight crews to exceed their allowed duty timings. This forces airlines to cancel or reschedule flights.
• Network Ripple Effect: A single delayed flight in Delhi impacts its subsequent routes. This requires airlines like IndiGo and Air India to arrange alternative aircraft.

Cascading National Impact

The Indira Gandhi International Airport is a critical hub. Its operational status directly affects the schedules of airlines nationwide. When fog hits, airlines issue travel advisories. They warn passengers of potential delays and cancellations. Air India, for instance, activates its “Fog Care” initiative. This offers complimentary rescheduling or full refunds to affected passengers. The industry is continually working to improve resilience. For the latest commercial aviation news, check flying.flights.

• Key Mitigation: Delhi Airport has three CAT-IIIB compliant runways to handle low visibility.
• Operational Barrier: Delays are often caused by non-CAT III compliant aircraft or pilots.
• Regulatory Window: The DGCA officially designates December 10 to February 10 as the winter fog season.