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Design plays a key role in the competition between the UK's regional airports and London's big four — Heathrow, Gatwick, Stansted and Luton. Bristol International Airport's eye-catching £27m terminal building was opened by Princess Anne earlier this month as the most recently completed expansion of a regional airport. Advertised as "the gateway to Bristol and the West Country", it looks like a budget version of Stansted, complete with clear-glazed window walls and an oversailing roof supported on branched steel trees.

"The old terminal was not very memorable, and the client wanted to change perceptions," says Jonathan Gray, managing director of architect YRM. "They wanted to capture those passengers who normally drive straight past Bristol airport to Heathrow or Gatwick. So, we had to establish a style that would be recognised as suitable for international travel."

At Newcastle International Airport, a £27m extension, which opened in January, has also been conceived as a regional gateway to compete with the more dominant Manchester Airport. Here, Crispin Wride Architectural Design Studio, also working to a tight budget, has produced an elegant and airy pair of halls beneath aerofoil-shaped lightweight steel roof trusses, although Crispin Wride admits that the halls are essentially two simple boxes.

Also essential in attracting customers is a calm and clear building layout that reduces the inevitable stresses of air travel. Both terminals have clear-glazed window walls to admit maximum daylight and provide views, while the Bristol terminal is covered by a regular grid of pyramidal rooflights — another Stansted trick.

As for internal layout, passengers must be able to find their way through the terminal without confusion. "The best layouts should be self-evident, with no need for signage," says YRM's Gray. "So, we have gone for transparency in every sense."

In most latter-day regional air terminals, including Bristol and Newcastle, the various functions are logically arranged in three parallel strips. The main check-in concourse is inevitably located on the landside, while the departures lounge and arrivals baggage reclaim overlook the runway. An intermediate zone containing passport and customs controls, toilets, services and vertical circulation is usually sandwiched between the two.

At Bristol, the three strips are housed within three rows of identical structural bays measuring 21.6 m square. At Newcastle, the airside and landside accommodation are similarly housed beneath trusses with a clear span of 27 m, but the central services are contained within a narrower 12 m wide strip that doubles as a rigid backbone to stiffen the entire superstructure.

Despite these compact, logical layouts, passenger flows are not as straightforward as they might be. Circulation is deliberately made more tortuous so that passengers can be ensnared by one of the airport operating companies' main moneyspinners – retail.

"There is a need to string out the separate operational and commercial functions," explains Wride. "The effect is that passengers end up zig-zagging through the building."

At Newcastle, passengers are directed through a cluster of shops on their way to the long pier to the waiting aircraft. At Bristol, shops and a restaurant are housed in a mezzanine to the upper floor directly beneath the roof trusses.

On a purely functional level, "the key issue of air terminal design is to cater for continual growth," says Wride. His extension, designed in association with his practice's parent engineering firm, Gibb, is the first phase of a four-phase masterplan to cope with airport growth over 20 years. All four phases have the identical form of a double shed with central service zone, and these can be strung together end to end. Bristol's new terminal of identical bays is similarly extendable at either end.

Adaptability for inevitable changes in layout is no less vital; hence the use of wide-span structures that will not get in the way of internal rearrangements.

The need to minimise disruption to airport operations also points to prefabricated construction. Both the Bristol and Newcastle terminals have used lightweight prefabricated steel trusses and cladding panels that could be craned quickly into position with the minimum of messy wet trades.

Finally, clients are becoming increasingly aware of the need to cut ongoing energy and maintenance costs; hence the high level of natural daylighting through wall and roof glazing. And, at Bristol, the lofty halls are comfort-cooled by an energy-saving displacement system. In addition, the oversailing roof canopy shades the perimeter window walls from excessive solar gain.

The design of regional airport terminals is a matter of balancing commodity, firmness and delight. And doing so on a budget.