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.''

Fire tenders put out a fire in an Air India Delhi to San Francisco (Boeing 777) flight at Delhi airport on April 24.

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

The APU is the smallest engine on an aircraft and 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 flight has been postponed, tweeted Air India.

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

“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, the national carrier said in a statement on April 25.

“There was no traces of any burn or external damage noticed except for the minor oil leaks traces, which was normal," it said.

Detailed inspection is going on, it added.