The Heathrow options
“Mixed mode” – not permitted at present, though trials began at the end of last year - refers to using both of Heathrow’s parallel runways for take-off and/or landing simultaneously.
Today, one is used for take-offs, the other for landings, which creates inefficiency when, for example, there are lots of departures waiting but relatively few arrivals, because the landing runway is then under-used, or vice-versa. If both runways were allowed to be used for both landing and take-off at all times, maximum use of Heathrow’s runways could be made.
The present system of separating the functions of the two runways is designed to give local area residents a little respite from aircraft approach or departure noise. This is done by alternating the use of the two runways, switching the function of each at a certain time every day.
According to Heathrow operator BAA, being allowed to offer mixed mode would generate extra movement opportunities at times of day/year when demand is lower, but fewer when demand is higher because capacity is then saturated, as it is most of the time.
And UK air navigation service provider NATS says that the theoretical maximum 15% runway capacity that mixed mode could unlock could be realised only if airspace use in the UK’s south east were allowed to be radically redesigned, and permission for that is not a foregone conclusion because of noise and ecology considerations.
Another constraint on Heathrow runway capacity is that - unusually for a major international hub airport - Heathrow has a local curfew between 23:30h and 05:00h each night, but no political party is suggesting its suspension because of the airport’s proximity to densely populated urban areas.
A steeper approach – for example 4deg rather than the international standard 3deg – would have the effect of reducing perceived noise in residential areas below the approach glidepath, but it would have no effect on increasing runway utilisation unless the glideslope change were accepted as a part of a deal for allowing mixed mode. There is no equivalent improvement available for departures.
An alternative or additional option for reducing approach noise would be to displace the runway landing thresholds further along the runways, effectively shortening them. This would increase the height of approaching aircraft above any given point on the approach path. British Airways has suggested this as a viable option because Heathrow’s runways are much longer than most modern aircraft require, but again, it is a noise-control measure and would provide no increase in runway utilisation.
The number of people carried in the average aircraft movement at Heathrow has been creeping slowly upward over the years, but this has been a result of market change and commercial decisions, not policy. Airlines say they can only operate efficiently if they tailor their aircraft capacity to demand for each route or departure.
The suggestion of reducing the daily or weekly frequency on certain popular routes but carrying the same number of passengers by using larger aircraft does not work commercially, because frequency – and therefore convenience - is a commodity that passengers - particularly business travellers - are prepared to pay for. The airlines argue that a frequency reduction tends to drive passengers to competing airlines with higher frequencies.
Also, essentially, a hub airport draws in connecting business because of the choice of flights it offers travellers who cannot travel direct from their local airport to their chosen destination. Dubai and Singapore are probably the best examples of how hub airports work. They do far more business than their indigenous populations could possibly support, benefiting their national economies through the heightened global connectivity they can offer companies there. Heathrow does the same for London and the UK south east, but capacity no longer allows for demand to be met.
As an example of the hub effect in the UK, Edinburgh airport’s catchment area cannot support departures to locations like Dubai, so residents there need single-aisle connectivity to Heathrow where they can catch a Dubai flight. If a suitable Edinburgh-Heathrow narrowbody departure is not available, the traveller will make the Dubai connection via one of the mainland European hub airports, improving the hubbing efficiency of that airport.