India’s biggest airline grounded at least seven Airbus SE jetliners as it awaits fixes for balky Pratt & Whitney engines, joining several carriers around the world that have pulled the planes from service.

IndiGo stopped using one A320neo aircraft this month after grounding four in June and two in May, according to data from flight-tracking website Flightradar24. Including IndiGo’s planes, there are 12 A320neos now out of service across five airlines worldwide, said a person familiar with the matter, who asked not to be named because the information isn’t public.

“We are aware that a limited number of Pratt & Whitney GTF-powered A320 aircraft are temporarily out of service for engine upgrades,” the engine maker said in a statement. “We are working with Airbus and our airline customers to ensure that any disruption involved will be minimized.”

Pratt, a unit of United Technologies Corp., has been working to fix durability issues and production snags that have hampered the roll-out of the engine, which was selected to power new jets from Airbus, Bombardier Inc. and Embraer SA. Airbus deliveries have been affected amid problems with engine parts, including the carbon seal and combustor liner.

For IndiGo, a lack of spare parts for Pratt’s new geared turbofan has been compounded by a new Indian tax on goods and services, which has made importing products more difficult, said a separate person familiar with the matter.

‘Operational Disruptions’

The airline, which is the world’s biggest customer for the A320neo with 430 on order, said in a statement that it “faced some issues with the neo engine, causing operational disruptions.”

Japan’s ANA Holdings Inc. and Hong Kong Express Airways Ltd. are also among airlines that have have grounded some aircraft recently.

“The A320neo and its GTF engine option, being a new aircraft type as well as a new engine type, require time to mature in their operational reliability,” HK Express, which has had one of its three A320neos under maintenance since June, said in a statement. ANA is operating one aircraft while the other one is undergoing maintenance after issues with both its engines, Youichi Uchida, a company spokesman, said by phone.

Airbus is working with the engine maker to ensure disruptions for airlines are minimized, it said in an emailed statement. Pratt said it received certification in April for a fix to the carbon seal issue.