Fire crews put out a fire in an Air India's plane at Delhi airport on April 24.

The fire started at Auxiliary Power Unit (APU) of the plane and was doused immediately.

The APU is the smallest engine on an aircraft and is situated at the tail of it. It provides the necessary power to start the main engines.

Air India called it a minor incident and said the plane was empty at the time of repair work.

The aircraft was bound for a flight to San Francisco that has been postponed, tweeted Air India.

A spokesperson of the airline said that an engine of the aircraft experienced an auto shutdown during technical inspection.

In a statement on April 25, the national carrier said: ''Airport personnel observed black fumes from the APU exhaust and, believing it to be a fire hazard, sprayed APU and part of the fuselage with foam spray.''

''There were no traces of any burn or external damage noticed except for the minor oil leaks traces, which was normal.''

''An investigation has been launched to find out the causes of the fire.''