That can mean thousands of extra travellers unexpectedly turning up at terminal search areas.
Edinburgh Airport said it had to cater for up to 10 per cent more or fewer passengers than forecast – or around 2,000 extra a day.
Glasgow Airport managing director Mark Johnston said: “We get no passenger numbers information from airlines. There is a lot of variability when we plan for security. The business traveller will arrive at the very last second, while charter passengers will arrive up to five hours early because they want a party.”
A spokesperson for AGS Airports, which also runs Aberdeen and Southampton airports, said: “We don’t receive exact information such as load forecasts from our airline partners, and they are under no obligation to do so. We use a wide range of methods including historical data analysis and flight-specific passenger behaviour profiling to help identify trends.
“This allows us to estimate the number of passengers we can expect at any given time to put the correct resources such as security staffing levels in place. Our forecasting accuracy from a security perspective has never been below 95 per cent.”
A spokesman for Edinburgh Airport said: “Our passenger projections are robust and provide at least 90 per cent accuracy, which allows us to plan for flows and movements days, weeks and months in advance, while data from airlines can fluctuate depending on late bookings and cancellations.
“Those changes would require regular updates to our modelling which is already flexible enough to cope with any late change.
“We work closely with all of our airlines, especially around major events such as the Six Nations rugby weekends, when we see additional flights and a larger influx of passengers. This dialogue allows us to work together and plan ahead to ensure the passenger experience is as positive as possible.”
A spokeswoman for Flybe said: “Airports have access to a selection of numerical data and statistics to assist them with projected passenger numbers on any particular day, including that based on known published schedules and historic passenger numbers through the airport.”
EasyJet said: “We provide passenger loads for flights to the airport the day prior to departure.”