Astonished Delhi residents have experienced dense fog on Friday morning with minimum temperature settling at 11.5 degrees Celsius. First fog during the ongoing winter has reportedly fumbled flight operations at Delhi Airport with delays, diversions and flight disruptions across the domestic network.

More than 130 trains have been cancelled and 60 early morning flights have been forced to commence delay because of the fog. A fall of two or three degrees Celsius in minimum temperatures has been predicted to appear over the region from January 9, Thursday. Shallow to moderate fog may occur at isolated places over Punjab, Haryana, Chandigarh, Delhi and west Uttar Pradesh.

The meteorological department has forecast a partly cloudy sky and moderate to dense fog early on Friday morning in Delhi. Very light, isolated drizzles have also been expected in the city today. On January 13, the met office is expecting partly cloudy sky with thundery development reports The Times of India.

The Indira Gandhi International Airport (IGIA), countrie's busiest one, handles around 900 flights a day and is the lone equipped with CAT IIIB Instrument Landing System. However, between 4 am to 10 am visibility has been recorded around 75 meters and no plane could take off during that period.

The Airport Authority of India (AAI), responsible for controlling air traffic movement at all civil Indian airports has promised to bring the situation under control soon. Facilities in dense fog witnessing airports like Lucknow and Amritsar have been upgraded to CAT II from CAT I Instrument Landing System (ILS).

CAT I ILS guides pilots in landing aircraft in visibility up to 550 meters, while CAT II can afford landing in visibility of up to 350 meters. The Delhi airport is equipped with CAT III- B ILS, which is capable of functioning in visibility up to 50 meters.

The calibration of the ILS has been completed and the Directorate General of Civil Aviation initiated certification for operations. However, visibility at Lucknow, Amritsar, Varanasi and Gaya has reportedly gone below 50 meters due to dense fog, reports The Hindu quoting Dr. R.K. Jenamani, Head of the IGIA Met office.

Up gradation to CAT IIIC instrument landing facility has been demanded by Amber Dubey, Head of Aerospace and Defense Practice at KPMG said.  Some operational factors have been cited as the logical reasons for up gradation to CAT IIIC which allows pilot to land in complete blindness, reports Business Standard.

Refreshments have been reportedly served on board and guests kept updated on the status of the flights. Guests have also been offered refunds as per policy and DGCA civil aviation regulations or accommodated on subsequent flights.

The Indira Gandhi International Airport (IGIA) has been compelled pausing air traffic movement for around six hours. Authority's move for upgrading ILS up to CAT IIIB (allows to take of in visibility up to 75 meters) has gone in vein. Met office predicted thundery developments may cease flight operations even for a longer period.