Switzerland's main airport hub may need to expand to cope with a predicted increase in flight movements that could outstrip capacity in 12 years.
A report, commissioned by the Federal Civil Aviation Office (FOCA), projects a rise in take-offs and landings at Zurich airport from today's 266,700 to 350,000 in 2017 and 450,500 by 2030.
The current capacity is 350,000 flight movements a year.
Passenger numbers are predicted to more than double from the current 17.1 million per year to 39.9 million in the next 25 years, according to the study from Munich company Intraplan.
Zurich airport's three runways would not be sufficient to cope with such an increase in traffic, operators Unique told swissinfo.
And FOCA, which is currently reviewing commercial air transport in Switzerland, said in a statement that building a new runway at Zurich airport would be necessary if the report's projections were borne out.
"For traffic to develop to the forecast future maximum capacity, according to these findings it will be necessary in the medium- and long-term to expand the infrastructure (build a new runway)," the statement reads.
A spokesman added that a variety of other social, economic and environmental factors would be considered when determining the sustainable development of air transport in Switzerland.
Aviation expert Sepp Moser told swissinfo that the best-case scenario report should be taken with a pinch of salt. And he warned that the prospects of building a new runway at Zurich look bleak.
"Predictions are always difficult and no-one really knows what will happen. If we have an outbreak of avian flu then the global aviation industry may collapse, but if we have a big economic recovery then it may grow rapidly," he said.
"Zurich airport's runway system is inherently ineffective because the runways or approach paths cross each other. But it is topographically almost impossible to build another runway because there are hills all around."
Moser added that such a plan would not be welcomed by residents living near the airport.
Several anti-noise pollution protest groups have been set up since Germany banned flights over the southern part of the country in 2003, increasing the number of approaches over Swiss skies.
"Any change in the runway system must be submitted to a public vote, and the way the mood is right now, it would be impossible to get the go-ahead," said Moser.
"Anyone who owns more than 100 square metres of land in the vicinity of the airport seems to have set up some kind of resistance organisation against noise pollution."
swissinfo, Matthew Allen in Zurich
Annual flight movements are projected to rise from the present 266,700 to 401,900 in 2020 and 450,500 by 2030.
Passenger numbers are predicted to grow from 17.1 million per year to 31.9 million in 2020 and 39.9 million in 2030.
The Federal Civil Aviation Office is currently reviewing commercial air transport in Switzerland and will present its findings in 2007.