The directorate-general of civil aviation has removed four of its flight operations inspectors, who monitor airlines’ compliance with regulatory and safety norms, following the large-scale IndiGo flight disruptions this month.

IndiGo on Friday announced the appointment of an external aviation expert to review and assess the recent operational crisis.

A statement from the aviation regulator said: “...The following FOls under various categories, on contract basis, in DGCA are hereby relieved from DGCA with immediate effect to join their respective parent organisations.”

Sources confirmed that these four officials, hired on contract from the aviation sector by the DGCA, had been removed in connection with the IndiGo mayhem.

Flight operations inspectors are senior officials who are part of the DGCA’s regulatory and safety oversight regime, and are often deployed to monitor airline operations.

They ensure aviation safety by inspecting, auditing and certifying that airlines and personnel — such as pilots, dispatchers and cabin crew — do meet the regulatory standards. They are expected to oversee training, flight standards, and accident prevention measures.

IndiGo announced that it had appointed a consultancy — Chief Aviation Advisors, led by Captain John Illson — to ascertain the root cause that led to thousands of its flights being cancelled or delayed since December 2. It said this would also provide opportunities for improvement.

Captain Illson has more than four decades’ experience working with the US Federal Aviation Administration, International Civil Aviation Organisation and the International Air Transport Association, apart from major global carriers.

“With an illustrious track record in global air transport, he (Illson) brings extensive expertise in global aviation strategy, customised consulting, safety leadership, setting international standards, and new aircraft technologies,” IndiGo said.

The decision follows a recommendation from IndiGo’s crisis management group, constituted by the airline’s board, to commission an independent expert review.

“With the board’s approval now in place, the review will begin at the earliest, and the independent expert reviewer will submit a comprehensive report to the board upon completion,” an IndiGo spokesperson said.