Airlines should not keep passengers seated inside aircraft for more than 90 minutes in case of fog-related delayed departures and they need to cancel flights delayed by over three hours. As peak winter fog season kicks in, the Union civil aviation ministry on Wednesday listed dos and don'ts for airlines and airport operators to minimise passenger inconvenience.The Bureau of Civil Aviation Security's (BCAS) circular for facilitating smooth re-entry of passengers in case of flight cancellations was operationalised and drills were organised by CISF with stakeholders. This would significantly reduce passenger inconvenience and ensure a smoother re-boarding process once flights resume, the Ram Mohan Naidu-headed ministry said in a statement. Airlines have been instructed to proactively communicate with passengers about potential delays/cancellations due to visibility issues. For this, airlines and booking agents (need) to ensure that correct passenger contact information is recorded during ticket booking.The Met department (IMD) along with Airports Authority of India (AAI) is expediting implementation of advanced weather observation system (AWOS) at Indira Gandhi International Airport and other fog-affected airports. This system will ensure accurate and timely weather information for pilots and air traffic controllers to enhance operational safety and efficiency. IMD (is) committed to ensure all Met equipment function without disruption.The Directorate General of Civil Aviation (DGCA), in close coordination with airlines, has ensured deployment of adequate number of CAT II/CAT III-compliant crew and aircraft to carry out low visibility operations efficiently during fog at affected airports. Three runways at the Delhi airport have activated CAT-III ILS systems, including the important runway 10/28 (the one between T1 and T2.Airlines have been asked to ensure full staffing at check-in counters during peak hours to reduce passenger inconvenience. Delhi airport has installed LED screens at prominent locations to provide real-time updates on visibility conditions. The airport has also scaled up the number of 'follow me' vehicles, which will guide and assist the pilots on the apron/taxiway during low visibility conditions ensuring better coordination on ground, the statement says.