MUMBAI: An initial probe by the apex aircraft investigation body AAIB has found that one of the Pratt & Whitney-powered engines of the A320 Neo flight of IndiGo, which had made a turn back to Pune early this month, stalled mid-air with a loud bang, according to sources.
The investigation into the incident that took place on April 2 were handed over to the Aircraft Accident Investigation Bureau (AAIB), after a preliminary probe by the aviation regulator Directorate General of Civil Aviation (DGCA).
The bureau has the mandate to investigate all serious incidents/accidents involving aircraft.
The Pune-Nagpur flight being operated by an A320 Neo plane (VT-ITG) was later grounded at the Pune airport as it required a major engine overhaul.
"While climbing out of FL150 (15,000 ft), a loud bang was heard by the crew which was followed by one engine stalling and high EGT (exhaust gas temperature) going over the limit," the AAIB said in its initial probe.
The report has been shared with the French aviation authorities.
The preliminary report also found damages to the engine's low-pressure turbine (LPT), which forced the pilot to return to Pune.
Significantly, IndiGo spokesperson on April 2 had termed the incident only as an 'engine caution message," while the incident was a grave safety risk as per the bureau report.
"After take-off from Pune for Nagpur, the pilot observed engine caution message in the flight (6E-134) operated by an A320 Neo plane. Following this the aircraft returned to Pune," the spokesperson said even without admitting that the plane was a P&W-powered A320 Neo.
When reached for comments on the AAIB probe, the airline Friday said as a "matter of policy" it does not comment on an on-going investigation and parried a query on why such a serious incident was dubbed as simply engine 'caution" message.
"We immediately reported the occurrence as per the laid down SOP to the DGCA. Subsequently, the matter was also referred to the AAIB, whose investigation is still on," Indigo said in the statement.
The US engine-maker Pratt &Whitney, which has been assuring DGCA of fixing the numerous issues its engines face for the past three years now, did not respond to a PTI query on the issue.
The A320 Neos of IndiGo and GoAir, which are fitted with P&W engines have been facing glitches intermittently, including mid-air engine shut-downs since their induction in the fleets of these carriers over three years ago.
The DGCA only recently conducted a special safety audit on IndiGo for alleged several lapses, non/ irregular reporting of incidents and had issued show-cause notices to its chief operating officer and the head of its engineering.
IndiGo, however, claims that its "operations are run more stringent than the prescribed regulatory framework."
Significantly, the now grounded Jet Airways, as also SpiceJet and Vistara had flagged serious concerns over the data on technical snags faced by them since 2017, which was provided by the government in Parliament.
"The number of technical snags being reported by various airlines is inaccurate. This discrepancy and misreporting of data is leading to false illusion of the relative safety of some airlines over other,' the troika had said in a letter to ministry in March 2018.
It came after IndiGo with a fleet size of 151 and over 1,000 daily flights, at that time, had reported only 340 technical snags, of the total 24,700 glitches reported by all carriers for in 2017.
Later in July 2018, the airline revised these numbers by a manifold to 14,628 from just 340.