The airline has already grounded the four pilots and set up an internal probe into the incident, which took place about four years ago but was brought to the notice of the Directorate General of Civil Aviation (DGCA) only this week.
"IndiGo has informed DGCA of grounding of the four pilots and setting up of an internal enquiry. We will seek their investigation report first before mulling an action against them," DGCA sources said.
However, IndiGo, while confirming that it has put these pilots off duty, said they were travelling as regular passenger on one of its international flights.
"It is learnt that our four pilots who were travelling (in October 2013) as regular passengers have been alleged for clicking picture holding a bottle of alcohol (which was sealed) inside the aircraft ... this matter was thoroughly investigated by the concerned department internally," an IndiGo spokesperson said.
Rule 24 of the Aircraft Rules, 1937 prohibits crew members from taking alcoholic drinks 12 hours prior to the commencement of a flight. As per rules, the flying license of a crew member found drunk on duty would be suspended for three months. Their license could be suspended for two years for a second offence and five years if they are caught a third time.
Action, other than suspension, can also be taken for the violation of the rule."As per the internal investigation and records, these pilots were on leave and were off duty hours, when this picture was clicked by them as regular travelers on an international flight," the spokesperson said.
Citing a particular DGCA ruling, IndiGo said the rule permits photography inside the aircraft, adding, "the said pilots were not in uniform in the picture and it was an international flight where consumption of alcohol is not prohibited."