As it prepares to implement the long-term master plan that mainly focuses on meeting growing passenger numbers, DIAL has also asked airlines operating from T1 to partially shift their operations to T2 from October.
No-frills airline IndiGo, SpiceJet and GoAir operate from T1, which handled around 24 million passengers in 2016-17 whereas its rated capacity is 20 million passengers per annum.
"We have planned to increase the capacity of T1 and T3 and build a fourth runway in due course of time," Delhi International Airport Ltd (DIAL) CEO I Prabhakara Rao told reporters in Delhi.
As per the master plan, capacity of T1 will be increased from 20 million to 40 million and the capacity of T3 will be increased from 34 million to 45 million, he said in a statement.
Departure terminal T1D would be merged with arriving terminal T1C and then expanded to accommodate 40 million passengers per annum.
A fourth runway would be constructed by 2021. "This will ease out future pressure on other runways and will be constructed parallel to runway 11/29," DIAL said.
At present, there are three runways -- 11/29, 10/28 and 9/27.
The Indira Gandhi International Airport is the busiest in the country, handling 57.7 million passengers and more than 8.57 lakh tonnes of cargo in 2016-17.
Taking into consideration rising passenger numbers, Mr Rao said, "We have asked the airlines operating from T1 for part shifting of operations to T2 from October".
There is an immediate need to decongest T1 and one-third of operations need to be shifted to T2, which has been revamped with an investment of around Rs 100 crore, Mr Rao said.
Operations at T2 were stopped in 2010. Once the work is completed, operations from T2 would be shifted back to T1. After that, T2 would be demolished and a new terminal T4 will come up there, he said.
Currently, there are two operational terminals at the airport here -- T1 and T3.
"In the last eight months, multiple (rounds of) discussions have happened and finally, we decided that one- third of traffic should have to move to T2," Mr Rao said.
The airlines have to decide which routes they want to offer from T2, he told reporters here, adding that shifting has to be done by October.
There would be a "huge transformation" for T1, Mr Rao said, adding that there would be metro rail connectivity to the terminal.
Under T1 expansion plan, the area would be increased to 1,69,000 square metres from 60,000 sqm.
The number of entry gates would be increased to 13 from 8 while the parking stands would go up to 82 from 71, among others.
An Eastern Cross Taxiway would also be developed that would help in reducing the occupancy of the runways. This would in turn help increase the number of flight movements.
Without divulging financial details about the proposed expansion plans, Mr Rao said work at T1 is expected to start by March next year.
At present, the airport sees an average of 1,200 flight movements everyday.
The expansion activities are part of the master plan, which would be implemented in three phases starting from 2018 -2021 period.
The work in the second and the third phases would be done during 2021-2025 and 2026 onwards, respectively.
After the 2006 master plan, there have been changes in operating conditions, including the growth of low cost carriers, growth of transfer traffic at the airport and increase in volumes of belly cargo.
Belly cargo refers to the cargo carried in the belly of an aircraft.
"Keeping in view the unprecedented growth at Delhi airport and future infrastructure requirements, master plan 2016 has been reviewed and accordingly revised master plan 2016 has been developed," DIAL said.
DIAL is a consortium led by the GMR group. Other stakeholders are government-owned Airports Authority of India (AAI) and Germany's Fraport.
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