New Delhi: The country’s biggest discount airline IndiGo, run by InterGlobe Aviation Pvt. Ltd, has sought in-principle approval from the civil aviation ministry for a possible future order of 150 aircraft.

The carrier wants approval “for import/acquisition of an additional 150 aircraft for scheduled air transport," it said in a letter to the ministry that has been reviewed by Mint. The airline had ordered 100 Airbus A320 jets in 2005, deliveries for which will run till 2015.

The civil aviation ministry isn’t opposed to giving in-principle approval, but the airline will have to seek permission from the government when it actually orders the aircraft and starts importing them, said an official who did not wish to be named.

Adding aircraft: IndiGo’s current order of 100 Airbus A320s will take until 2015 to be completed.

IndiGo told the ministry that 30 of the 100 A320 planes it had ordered in 2005 had been inducted.

“The remaining 70 aircraft are going to be inducted in a phased manner over the next five years as scheduled," IndiGo said in the letter to the civil aviation ministry.

The move comes soon after the carrier hired four international investment banks to help it raise funds this year to finance expansion plans that include the proposed start of overseas flights.

UBS AG, Morgan Stanley, Credit Suisse Group and Citigroup Inc. were hired this month by the airline to raise money through either an initial public offering (IPO) or the private equity route, as Mint reported.

The airline had also sought in-principle approval from the ministry earlier this year to fly overseas, a request which is still pending.

It completes five years of operations next year, which allows it to operate international flights, as per the existing rules.