NEW DELHI (Reuters) - IndiGo INGL.NS must replace all Pratt & Whitney (P&W) engines on its fleet of almost 100 twin-engined Airbus A320neo family aircraft with new P&W power units, India's air safety watchdog said on Friday following recent inflight engine shutdowns.

FILE PHOTO: The logo of IndiGo Airlines is pictured on passenger aircraft on the tarmac in Colomiers near Toulouse, France, July 10, 2018. REUTERS/Regis Duvignau

The incidents have caused “serious concern” and the decision to order the engines be replaced was taken after “considerable deliberations,” the Directorate General of Civil Aviation (DGCA) said in a statement.

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

“This situation cannot be allowed to go on indefinitely,” it said, adding that the engines would need to be replaced by Jan. 31, 2020.

IndiGo is Airbus' AIR.PA biggest client for A320neo planes.

While the United Technologies' UTX.N Pratt & Whitney engines are fuel efficient there have been issues since they entered into service in 2016, forcing the airline to ground its planes several times.

The groundings have cost IndiGo, which last month posted its biggest-ever quarterly loss after being forced to lease aircraft to replace planes grounded with engine issues.

IndiGo said it currently operates a fleet of 98 A320neo family planes in which around 45% of its engines are modified.

“We are working with both P&W and Airbus on mitigation so that we have enough modified spare engines by January 31, 2020. In the meantime, our schedule remains intact,” it said in a statement to stock exchanges.On Monday the DGCA ordered IndiGo and domestic rival GoAir to modify 29 Airbus A320neo aircraft fitted with Pratt & Whitney engines within 15 days to avoid them being grounded.

The DGCA said that planes fitted with Pratt & Whitney 1100 series engines that have clocked more than 2,900 hours must have at least one modified engine, impacting 16 of IndiGo’s planes.

In its statement on Friday, the DGCA said 7 more of IndiGo’s planes have been found to have the same issue taking the total to 23. It has asked the airline to replace at least one engine on these 23 planes by Nov. 19 and IndiGo would then need to replace both engines on its entire A320neo fleet.

DGCA chief Arun Kumar, who was recently appointed to the position, is making the right decisions relating to safety, said Kapil Kaul, India CEO at consultancy CAPA.

“This gives time for these engine changes to be completed and yet remains firm on safety,” said Kaul, adding that Pratt & Whitney would need to ensure that all engines are replaced by the deadline.