 The availability of airport capacity has been identified as an important constraint on the ability to meet the increasing demand for air travel . In many cases airport capacity is already fully used in meeting current demand . At Heathrow and Gatwick airports the runways are full for " … virtually the whole day " . In 2003 the runway at Birmingham airport was expected to reach full capacity by 2009 at the latest , whilst terminal capacity at Edinburgh airport had reached its limit . Government forecasts that year predicted that by 2030 the number of passengers could rise to between 400 million passengers per annum ( mppa ) and 600 mppa , representing a two to threefold increase , and a figure of 500 mppa by 2030 was regarded by the government as robust . In 2006 the government reported that at 228 mppa the demand for air travel the previous year was in line with the 2003 forecast , but also revised the forecast demand for 2030 downwards to 465 mppa as a result of capacity constraints , even taking into account proposed airport developments . 
