Why Delhi Airport faces delays despite of having CAT III-B tech?

Every winter, a thick blanket of radiation fog descends upon the Indo-Gangetic plain, turning Indira Gandhi International Airport (IGIA) into a high-stakes testing ground for aviation technology. While IGIA remains one of the most technologically advanced hubs in Asia, the persistent cycle of cancellations and delays raises a critical question: is the technology sufficient to match Delhi’s extreme climate?

The summer struggle: Thin air and physics

Before the winter fog arrives, Delhi’s aviation systems face a different enemy; extreme heat. When temperatures soar above 45°C, the air becomes less dense. This "Density Altitude" problem forces aircraft instruments to work overtime.

Aircraft rely on air pressure to calculate speed and altitude. In thin, hot air, wings generate less lift and engines produce less thrust. A pilot’s dashboard might indicate a safe takeoff speed of 140 knots, but the actual speed over the ground must be significantly higher to achieve flight. To prevent sensor failure, aircraft use redundancy systems, three separate computers that cross-check data from Pitot tubes. In Delhi, these sensors must also contend with heavy dust and PM2.5 particles, which can clog the delicate ports used to sense air pressure.

Winter’s radio-guided path

In terms to combat the fog that reduces visibility to a few meters, Delhi uses the Category III-B (CAT III-B) Instrument Landing System (ILS). This ground-based hardware transmits two radio beams:

1. The Localiser: It aligns the plane horizontally with the runway centerline.

2. The Glideslope: Used to guides the aircraft’s vertical descent angle.

On three of Delhi’s primary runways (10/28, 11L/29R, and 11R/29L), these beams allow for "Auto-Land" procedures. In this mode, onboard computers take control, flying the aircraft to the runway surface with minimal pilot intervention.

Then why the delays persist?

Despite having CAT III-B, which allows landings in visibility as low as 50 meters, the system has clear limits.

• If visibility drops below 50 meters, operations stop. While CAT III-C technology exists to allow zero-visibility landings, it is not currently in commercial use globally due to safety risks.

• Landing is only half the battle. Once on the ground, pilots must navigate a complex web of taxiways to reach the gate. In dense fog, even high-intensity lights are invisible. Currently, airports rely on "Follow-Me" vehicles, a manual process that slows down the entire system.

• During Low Visibility Procedures (LVP), Air Traffic Control (ATC) must increase the distance between aircraft to prevent signal interference. This reduces runway capacity by more than 50%, turning a 2-minute gap into a 6-minute wait.

Predictive AI: The new frontier

In late 2025, Delhi International Airport Limited (DIAL) integrated the Airport Predictive Operations Centre (APOC). This system uses AI and predictive analytics to merge real-time weather data with airside operations. By using data from the Winter Fog Experiment (WiFEX), the airport can now predict dense fog with 85% accuracy up to 36 hours in advance.

This shift from reactive to proactive management allows airlines to adjust schedules before passengers reach the terminal. Furthermore, new Advanced Surface Movement Guidance and Control Systems (A-SMGCS) are being upgraded to Level 3 and 4. These systems provide ATC with better surveillance of ground traffic, reducing the reliance on visual cues for taxiing.

While the technology at IGIA is reflecting to be of global standards, the human and physical elements, ranging from pilot certification to the sheer physics of zero visibility, ensure that technology is a tool for management, not a total cure for Delhi’s weather.