New Delhi, November 1: Stating that "desperate measures" were required to "put things in order", aviation regulator DGCA told IndiGo on Friday to replace the Pratt and Whitney (PW) engines under both wings of 97 A320neo aircraft "at all costs" by January 31 or they would be grounded.

Of the 97 aircraft, 23 have PW engines that have been used for more than 2,900 hours and have to be replaced in the first tranche by November 19, the Directorate General of Civil Aviation (DGCA) told the low-cost carrier. IndiGo, GoAir Barred From Flying Airbus 320neo Fitted With PW Engines to Port Blair Airport.

The DGCA directive came after the airline faced four mid-air engine malfunctions in A320neo planes in the last one week, which "has caused a serious concern and resultant disruption", according to the regulator.

The DGCA had, on Monday, asked IndiGo to replace the PW engines of 16 A320neo planes, which were used for over 2,900 hours, by November 12, but it subsequently found out that seven more aircraft were flying with such engines.

"Kindly note that after that (November 19), none of these 23 aircraft, which does not have at least one LPT (low-pressure turbine) modified engine on its wings, shall be allowed for commercial operation and their schedule will suitably be curtailed till this is accomplished," the regulator said in a press note on Friday.

With a fleet of 247 planes and a share of around 48 per cent of the domestic air passenger market, IndiGo is India's largest airline. Just three days after the company placed one of the single-largest aircraft orders with Airbus, the DGCA advised it on Friday to "stagger or defer your future (aircraft) induction plan and procure a sufficient number of modified engines to keep the existing fleet in operation".

On Tuesday, IndiGo had announced that it would buy 300 "Airbus 320neo family" planes, which comprised A320neo, A321neo and A321XLR aircraft.

However, the budget carrier made it clear that the choice of engine manufacturer for this order would be made at a later date.

On Wednesday, one of the PW engines of an IndiGo A320neo plane that was heading from Kolkata to Pune stalled mid-air, forcing the pilot to return to the Kolkata airport.

On three consecutive days from October 24 to 26, IndiGo had three in-flight PW engine shutdowns, compelling the DGCA to visit the airline's premises on Monday to review the maintenance and safety data.

"You (IndiGo) will appreciate that four successive events have not happened ever before and therefore, call for an urgent and effective action. We regret the inconvenience but we need desperate measures to put things in order," the DGCA said on Friday.

Later during the day, IndiGo issued a statement, saying, "We have received the latest directive from the DGCA on November 01, 2019, which requires that all operating A320neo should have both engines with LPT3 modification installed for operation post 31st January, 2020."

"IndiGo currently operates on its fleet of 98 A320 NEO family with around 45 per cent of its engines modified. We are working with both PW and Airbus on mitigation so that we have enough modified spare engines by January 31, 2020. In the meantime, our schedule remains intact," it added.