Aviation Fog at Delhi airport leads to 450 delays, 40 cancellations Updated : December 31, 2019 07:31 AM IST Airport sources told IANS these flights had to be diverted as pilots were not trained to operate in CAT IIIB conditions. 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. Dense fog and eventual poor visibility have caused flight delays and cancellations across north India in the past few days. Subscribe to Moneycontrol PRO at just Rs.33/- per month for the first year. Use code SUPERPRO. Limited period offer. Available on Web and Android.