In a major relief for IndiGo, the Directorate General of Civil Aviation has extended the deadline for engine replacement of its A320neo fleet till May 31 from January 31.

The task will need procurement of 135 engines as per an action plan submitted to the regulator DGCA by IndiGo, aircraft manufacturer Airbus and engine maker Pratt & Whitney.

"As per the initial count a total number of 120 modified engines were required to be placed on the fleet of M/s Indigo, however, this number is likely to be about 135, on account of additional removals resulting from stringent Boroscopic inspections and other reasons," DGCA has noted.

As of now, IndiGo has been able to place one modified engine on its entire fleet, ahead of March 2020 timeline set by European aviation regulator European Union Aviation Safety Agency.

DGCA expects about 70 percent of IndiGo's total Neo engines to be modified by January 31.

While the three stakeholders had asked the regulator to provide them time till June 2020 to replace Pratt & Whitney engines of its A320neo fleet as procurement was hit due to holidays during Christmas and New Year, DGCA has concluded that it can be compressed further and should be achievable by May 2020.

"Therefore, the revised timeline for the complete removal of unmodified engines from the fleet is May 31st 2020. It is further laid down that no Aircraft with the unmodified engine in Indigo fleet shall be allowed to fly after that," the regulator said in a statement.

In the matter of Pratt & Whitney engine-run A320neos, Indian regulator DGCA has been a step ahead of EASA by asking IndiGo to replace both engines till May 31. EASA as so far only asked airlines to replace at least one engine of A320neo with a modified one till March-end.

"Their AD (airworthiness directive) mandating complete removal is expected and may lay down the timeline," DGCA said.

In October and November 2019, the regulator had asked IndiGo to replace one of the two engines of 23 P&W-run A320neo aircraft (both engines of which have done more than 2900 FH). This was done to address the issues in the low-pressure turbine (LPT) which result in the breakage of LPT blades, engine vibration and then return of aircraft back to the ground. The regulator had intervened after four incidents of air "turn back" or "inflight shutdown" over the last week of October in the Pratt & Whitney-run A320neos.

As part of the investigation of events related to LPT damage, Pratt & Whitney has identified that fracture of Mid Turbine Frame (MTF) Piston seal is contributing to 50% of the LPT events.

To prevent potential damage to the LPT 3rd stage blades due to fracture of MTF Piston seal, P&W issued Service Bulletin dated 16th Dec 2019, to provide inspection criteria to perform a Boroscopic Inspection (BSI) of the piston seal for wear.

"This repeat inspection of piston seal Shiplap on engines having unmodified parts is considered to be effective in identifying and removing the engines before it fails on wing- as a short term measure. A number of engines have been removed based on these inspections," DGCA added.

As a result, DGCA has also asked the airline, engine maker and aircraft manufacturer to ensure that mitigation measures, such as the introduction of MTF Piston Seal in addition to the existing Boroscopic Inspections and introduction of Alt Climb Procedure, are put in place.