New Delhi: The aviation regulator on Monday grounded 11 A320neo aircraft - eight operated by IndiGo and three by GoAir - after another mid-air engine failure magnified safety concerns that have dogged one of the most popular, fuel-efficient, medium-range planes in the world.

PTI quoted a source as saying that "hundreds of passengers were stranded" after the flights were grounded. IndiGo said that "the affected passengers would be accommodated on other flights on our network. Safety is our top priority."

The decision to ground the 11 planes, fitted with a certain series of Pratt & Whitney engines, was taken after 186 passengers on an IndiGo flight from Ahmedabad to Calcutta via Lucknow had a mid-air scare when one of the engines failed.

The pilot of flight 6E-244 was forced to turn back a little over 40 minutes after takeoff, making an emergency landing at 10.04am in Ahmedabad.

Soon after the incident, civil aviation secretary R.N. Choubey said an "appropriate decision" would be taken later in the evening. Officials went into a huddle soon after and emerged with the directive to ground these A320neo planes.

"Keeping in view the safety of aircraft operations, Airbus 320neos fitted with PW1100 engines beyond ESN 450 have been grounded with immediate effect," the Directorate-General of Civil Aviation said. "ESN" stands for "engine serial number".

"Both IndiGo and GoAir have been told not to refit these engines, which are spare with them in their inventory," the DGCA said.

The A320neo is a fairly new plane, which began commercial operations in January 2016.

More than 240 Airbus A320neos are being flown around the world by 30 operators. IndiGo has one of the largest A320neo fleets with 32 aircraft. Not all of them are fitted with that particular series of Pratt & Whitney engines. GoAir has 13 such planes.