SpiceJet said its step ladder was well secured and with chocks in place.
"On June 6, a SpiceJet step ladder was parked on stand C87 (where one of our aircraft VT-SLA was parked) at the Mumbai airport. On stand C86, an IndiGo aircraft was parked. Both aircraft were not in service at that time," a SpiceJet spokesperson said in a statement.
"At around 7.30 am, sudden strong winds picked up. There was no prior weather warning or advisory. SpiceJet's step ladder, which was well secured and with chocks in place, was moved backwards and hit the IndiGo aircraft on the right wing," the spokesperson said.