The flight (AI-020) was scheduled to take off at 2.25 pm but left the Indira Gandhi International airport here at 6.11 pm, after the airline arranged an alternative plane.
"The delay occurred after one of the cooling units failed. Our engineering teams tried to replace the unit but when the problem could not be resolved, we arranged for an alternate aircraft.
"The plane that returned from Amritsar at 3.50 pm was the first aircraft that could be made available," an airline official said on the condition of anonymity.