Details of their responses could not be immediately known. Officials of the Directorate General of Civil Aviation (DGCA) are examining the replies filed by the three no-frill carriers on the show cause notices, official sources said here.
The DGCA had asked them to explain why they were carrying full-load of passengers and cargo to Patna and Jammu where they should have been flying with 20 per cent less load to ensure safe landing and take-offs on the small runways there.
The DGCA is shortly expected to strengthen the existing rules for operations to airports which have shorter runways and come out with specific instructions for the airlines to strictly follow, they said.
The aviation regulator had carried out real-time checks on flights of these three airlines to the two cities and found them carrying 170-180 passengers, instead of 150-155 as laid down in the Standard Operating Procedures (SOPs) for airports with short runways.
They had said that these airlines, in particular, were found to have been violating these SOPs almost on a daily basis to earn more revenue but endangering safety.
The three carriers were also asked to cancel bookings for the next few days if these were more than 150-155 to these two destinations.