American aerospace maker Pratt & Whitney on Monday said it was working closely with IndiGo and GoAir Airlines after the operators grounded eight Airbus A320neo planes following issues with aircraft engines.

Pratt & Whitney, owned by Connecticut-based United Technologies Corp, said some of the aircraft will be out of service temporarily due to the planned engine replacements.

Last week, IndiGo, India’s biggest low-cost carrier, grounded eight aircraft while smaller rival GoAir grounded three Airbus A320neo planes after issues with Pratt & Whitney aircraft engines.

The planes are expected to be back in service in the second half of August, IndiGo owner InterGlobe Aviation said in a statement.

Pratt & Whitney said separately it was planning to remove faulty engines and that it was retrofitting the Neo fleet with the latest configured engines.

The company is also providing spare engines to help airlines aircraft from August onward.