Budget carrier IndiGo`s Delhi-Mumbai flight had to perform a mid-air "turn back" manoeuvre due to excessive vibration from the aircraft`s engine number two, industry insiders privy to the development said on Friday. However, an airline official said that the aircraft had suffered a bird hit en-route from Delhi to Mumbai on Wednesday. The A320 NEO aircraft operated by IndiGo has faced a series of problems earlier with engine vibration being one of them. Industry sources said that at least 15 cases of mid-air engine problems have been reported in the A320 NEOs operated by IndiGo and GoAir since January.

Engine vibration resulting in mid-air turn backs has emerged as the most common and serious safety issue with the P&W engine powered NEOs of late. The country`s aviation regulator is said to be examining the incident. Wednesday`s incident comes days after the budget passenger carrier`s Delhi-Istanbul flight had to be diverted to Kuwait. The airline that time had said that an engine snag had hit its A320 NEO aircraft which was en-route from Delhi to Istanbul.