New Delhi, Dec 30 (TIWN) Dense fog-induced low visibility conditions led to the diversion of 20 flights from the Indira Gandhi International Airport (IGIA) here on Monday.

According to sources, these flights had to be diverted as pilots were not trained to operate in CAT IIIB conditions.

Reportedly, heavy fog had started to envelop the airport around 6 a.m.

"The low visibility conditions lasted from 6 a.m. to 12:30 p.m. during which 20 flights were diverted and 4 were cancelled. Landings and take-offs continued using CAT IIIB Instrument landing system during the period," sources said.

"After 12:30 p.m. the visibility improved to over 600 metres and the operations were shifted to CAT II."

The airport has technologically superior CAT (category) IIIB ILS system, which allows compliant aircraft and trained pilots to land even when the runway visibility is just 50 metres.

This year, new air traffic control (ATC) tower, thermal imaging cameras and first-of-its-kind 24X7 social media command centre are being used to manage operations during the reduced visibility conditions.

Consequent to fog, private airlines IndiGo and Vistara issued travel advisory for their passengers saying flights to and from the national capital have been impacted due to bad weather and poor visibility.