Dense fog hit operations at the Indira Gandhi International Airport here affecting over 160 flights, including that of External Affairs Minister Salman Khurshid.
Khurshid's flight, which was to take-off from Palam Technical area for Bhutan around 9.30 AM, was delayed by two hours due to fog.
Flight operations at the airport came to a standstill for around one-and-half hours, between 5 AM and 6.30 AM, as the runway visibility was less than 50 metres on both the runways, main (28/10) and third (29/11), airport sources said.
Around 130 domestic and international flights were delayed by over three to four hours after dense fog enveloped the airport and visibility become poor while 11 were cancelled.
Also 21 domestic and international flights to Delhi were diverted to Jaipur, Mumbai, Ahmedabad, Amritsar, Nagpur and Lucknow. Of these 11 were diverted to Jaipur, three each to Ahmedabad and Mumbai two to Amritsar and one each to Nagpur and Lucknow.
The flights were diverted as the visibility was less than 50 metres, which is the minimum required visibility for a flight to land using the most advanced Category III B (CAT-IIIB) of the instrument landing system.
According to sources, these flights were diverted as either their crew was not trained to operate in CAT-IIIB conditions or their aircraft were not CAT-IIIB compliant.
"This is in violation of clear cut instructions by the Director General of Civil Aviation to deploy CAT-IIIB compliant aircraft and pilots during the fog season," they said.
Smaller aircraft like turbo prop ATR, Canadian Regional Jets (CRJs) and Bombardier's Q400 turbo prop are not CAT-IIIB complaint, hence not fit to operate in dense fog conditions.
Eight flights coming to Delhi were diverted to Jaipur, Nagpur and Mumbai between 4 AM and 6 AM, when the runway visibility was less than 50 metres. Also no flights took-off between 3.30 AM and 6 AM due to which there was a huge backlog of flights, airport officials said.
An Air India flight, coming from Frankfurt - a Dreamliner - was diverted to Mumbai as the aircraft and crew is not CAT-IIIB rated by the DGCA.
The fog started to descend at the airport around 8 PM