Indian low-fare airline IndiGo, the first A320neo operator in Asia, has reduced its aircraft on ground (AOG) to two machines following operational disruptions involving the airplanes’ Pratt & Whitney PW1100G geared turbofans since early last year. As of October 18, the number of airframes in India awaiting spare engines had fallen from 15 to three—two with IndiGo and one with GoAir.

With 430 A320neos on order, IndiGo has yet to make a decision on the engine choice for a second tranche of 280 airplanes. However, with increases in fuel prices and the competitive environment in India, IndiGo might choose to operate the Pratt-powered airplanes for a longer period than its usual limit of six years, said IndiGo president Aditya Ghosh during a July conference call to discuss quarterly earnings. Ghosh cited a 15-percent lower fuel burn and “a much lower risk of technological obsolescence” in the PW1100G as factors in his decision.

Around 40 percent of the world’s geared turbofan-powered A320neos operate from India. Early adoptors have seen the benefit of lower fuel burn, but they’ve also witnessed entry pains involving an air system fault, extended engine start times and delivery delays due to fan blade production problems. In IndiGo’s case, the trouble with the Pratt engines “related to the premature degradation of the combustor chamber lining and the premature wear of the Number 3 bearing seal,” said Ghosh in July.

While the now-solved oil seal problem involved the global fleet, combustor lining degradation is an issue specific to India and Middle East, where particulates in the air also affected the PW1100G’s predecessor, the IAE V2500.

Pratt & Whitney has defined corrective actions for the combustor. The company introduced modifications first in mid-2016 and expects to introduce more into new production and overhauled engines starting at the end of the year.