Over a dozen flights were delayed at the Indira Gandhi International Airport on Tuesday morning due to dense fog.
"Fog become dense around 6 am and visibility dropped to below 100 metres on the new runway around 8 am, leading to delay in departure of around 15 flights," airport sources said.
The poor visibility on both the runways forced airport authorities to implement low visibility procedures on new runway (11/29) around 5.55 am and on main runway (10/28).
As visibility dropped further between 8 am and 9 am, departure of some of the flights had to be delayed, sources said.
However, low visibility procedures were terminated by 9.40 am.
The airport had on Monday witnessed delays in flight schedule after two of its radars went out of order.
In the second incident of radar failure within a span of four days, the air traffic controllers (ATCOs) failed to get position of aircraft approaching Delhi as the radar system was unable to process the data received from remote antenna at around 3.30 pm on Monday.
The long range radar (L-Band), which has a range of around 250 nautical miles and also called the route radar, is situated at the Bijwasan side of the airport.
Though the system was getting information from antenna, it was unable to process it and send it to ATCO consoles, following which a Notice To Airmen (NOTAM) was issued and maintenance work carried out.
In the meantime, the S-Band radar, also called the terminal approach radar and having a range of around 50-60 nautical miles, also developed the same problem.
This forced the ATCOs to instruct the pilots to follow a holding pattern and to hover for a while.
The ATCOs switched over to the manual procedural pattern in which they started communicating with the pilots through very high frequency (VHF) radio and helped them in safe landings, the sources said.
This led to delay in arrival and departures as the aircraft were landing in a gap of about seven minutes against three minutes.
The situation returned to normal after a gap of around five hours at around 8 pm, they said.