An engine of an empty Boeing 777 aircraft of Air India shut down at the Delhi airport on Wednesday night during a technical inspection, the airline said.Airport fire personnel then observed that black fumes were coming out of the engine's exhaust, following which they sprayed foam on it, Air India said in a statement on Thursday.

When an engineer was doing a routine technical examination of the empty aircraft (777) at the Delhi airport on Wednesday night, auto shutdown of the auxiliary power unit (APU) took place, the airline said. 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.

#WATCH Air India Delhi to San Francisco (Boeing 777) flight caught fire in Auxiliary Power Unit (APU) yesterday at Delhi airport. Fire started during AC repair. Air India terms it minor incident, plane was empty at the time of repair work, fire was doused immediately. pic.twitter.com/Og790FVABE

— ANI (@ANI) April 25, 2019

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. The APU was examined by opening its cowlings (cover). After opening the cover, "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.