NEW DELHI: The Directorate General of Civil Aviation (DGCA) has finally cracked the whip on Pratt & Whitney’s (PW) snag-ridden engines for the Airbus A320 new engine option (Neo) family of planes.IndiGo was on Friday asked to ensure that all the 98 Neos it currently has must get modified PW engines under both their wings latest by January 31, 2020. The Neos that do not meet this will not be allowed to fly beyond that date.Since IndiGo is the world’s largest customer for this aircraft and is yet to receive over 630 of them, the regulator has advised it to defer future deliveries so that the 98 Neos with it can get replacement engines - instead of new yet-to-be-delivered planes - and continue flying them beyond next February.“Last one week has witnessed four inflight shutdowns (of PW engines) and air turn back… has caused serious concern and resultant disruption. This situation cannot be allowed to go on indefinitely…. 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 did an unprecedented plain speaking to IndiGo.The airline has also been asked to change one engine each on 23 planes — instead of 16 as directed earlier — by November 19. These 23 planes have a more snag-prone type of engine under both their wings and the regulator will allow them to fly after November 19 only if they get at least one modified and less snag-prone PW engine each.The DGCA has also directed IndiGo that all of its current 98 Airbus A320 Neo family of planes must have both modified engines under their wings by January 31, 2020, to continue flying after that. “ In case it is not done, such aircraft shall not be allowed to fly with unmodified engines. You may like to stagger or defer your future induction plan and procure sufficient number of modified engines to keep the existing fleet in operation,” the letter to IndiGo stating this unprecedented action says.In a statement, IndiGo said: "DGCA had issued a directive last week as per which we are required to have at least one LPT 3 modified engine on aircraft which has one unmodified engine more than 2900 hours by November 19, 2019. We are confident that we are able to meet this directive and are able to sustain our current schedule. Subsequently, we have received the latest directive from the DGCA on November 1, 2019, which requires that all operating A320 Neo should have both engines with LPT3 modification installed for operation post January 31, 2020. IndiGo currently operates on its fleet of 98 A320 Neo family with around 45% of its engines 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."Alarm bells started ringing after four cases of PW engines on IndiGo A320 Neos stalled in climb phase (during take off) within a week. The regulator examined this issue threadbare and found unmodified or older version of PW engines that had flown for over 2,900 hours on the Neos were facing this issue.Accordingly, DGCA directed IndiGo and GoAir to change one engine on 23 and 13 of their Neos respectively which had both unmodified engines that had done over 2,900 hours within 22 days and 15 days, respectively. These 36 A320 Neos — that have the old PW engines which have flown for over 2,900 hours under both their wings — will be allowed to fly after the deadline only if one of their engines are replaced. This decision was taken after studying the pattern and evaluating the risk.On October 30, IndiGo 6E-862 -- flying from Kolkata to Pune saw a PW engine stall with a “big bang” and high vibration during take off and it then returned to land in Kolkata on one engine. While, IndiGo flight 6E-563 from Kolkata to Chennai returned to Kolkata on October 24 after reporting a snag. Similarly, on October 25, 6E-375 from Mumbai to Coimbatore and on October 26, 6E-329 Delhi to Goa, both returned to their origin airport after one PW engine stalled.Pilots in all these three cases did an inflight shutdown of the engines and returned to the airport they had taken off from on one engine.“India has the largest number of PW-powered Neos operating globally. So there is added responsibility on its aviation authorities to ensure safety of people flying on the PW-powered Neos of IndiGo and GoAir. We cannot wait for US Federal Aviation Administration or European Union Aviation Safety Agency (EASA) to take some decision and then act,” said an Indian pilot who flies the Neos.