A hijack threat note found in the washroom of a Mumbai-bound Air India flight before take-off on Wednesday morning prompted security officials to park the aircraft in an isolation bay of the airport here, an official said.The flight was scheduled to depart at 10.20 am.The note threatening that the plane would be hijacked at 11.10 am was found in the washroom just before the departure of the flight, Kolkata airport director Vikram Singh said.All the passengers who had boarded the aircraft were de-boarded, and it was taken to the isolation bay, he said.Security protocols were immediately activated, and the aircraft was moved to an isolation bay for a thorough inspection and necessary precautionary measures, he said.