The pilot of Flight SG-208, then overflying Gaya, sought priority landing from the Kolkata ATC, and safely landed there at 11.55 am.
The SpiceJet flight was taken to an isolation bay, where all 119 passengers disembarked.
An intensive check of the plane, its passengers and their luggage by CISF and bomb disposal squad personnel, however, found nothing suspicious.
Kolkata airport sources said the crew got suspicious about two passengers, Aslanbekov Artur, 43, and Irbaieva Eleonara, 32. They thought Irbaieva, who was wearing a burqa and was quite tall, might be a male, and their suspicion grew when she did not remove her veil while eating. They also allegedly heard her utter the word “hijack” at some point.
During interrogation, Aslanbekov and Irbaieva said they were a married couple from Russia, and Aslanbekov said he was a carpet trader.
They were due to take an Air India Express flight to Dhaka later on Wednesday.
When further questioning did not raise any red flags against the couple, they were allowed to proceed to Dhaka.
In a statement later, SpiceJet confirmed it had been alerted by the sky marshal on board, and that the security agencies were investigating.
The civil aviation ministry said no anti-hijack alert had been sounded.
Age Correspondents