“Due to foggy conditions around the runway, many international and domestic flights were delayed by two to three hours in the early morning,” a Delhi International Airport Limited (DIAL) official said.

In all, 12 flights which were either to depart or land were affected. These included flights from Frankfurt, London and other international destinations.

According to the official, despite low visibility procedures (LVP) being enforced for eight hours and six minutes, 226 flights were operated during the period under various ILS (Instrument Landing Systems) like CAT (category) - I, II, III A and III B.

“During the LVP, one international and 12 domestic flights were diverted,” DIAL's official statement said. Fog descended in the wee hours and the general visibility dropped below the required level of 50 meters forcing the airport authorities to implement the LVP.

“Fog appeared at 1.30 a.m. when visibility was at 700 meters and remained the same till 4.30 a.m. At 7.30 a.m., the visibility fell below the 50-meter-mark,” a Meteorological Department official said.

The DIAL official further said that the technologically superior CAT (category) IIIB ILS, which allows compliant aircraft and trained pilots to land even when the runway visibility is at 50 meters, could not cope up with the foggy condition below that level.

The capital, which experiences heavy fog from the third week of December to early February, had not experienced any significant fog till Friday, according to the IMD.