Today, it is beset by two-hour immigration queues, passenger numbers far beyond capacity and a crisis over management.

Immigration queues have grown so long travellers have been told to arrive three hours before a flight, an hour longer than in most air hubs, threatening to damage Thailand's tourist-friendly image.

The problems have become so acute in recent days that the government is trying to convince growing numbers of low-cost carriers to move operations to Don Muang, a domestic airport.

Airport of Thailand Pcl AOT.BK expects Suvarnabhumi to handle 51 million passengers this year, well above its capacity of 45 million, suggesting little relief for chronically overcrowded arrival and departure halls.

The immigration bureau has in the past blamed long queues on a staffing shortage. An official at Suvarnabhumi's immigration division, however, said it had more to do with lack of space.

"There's construction going on which is limiting the space we have available for security checks," he said, declining to be identified.

But travellers grumble at the frequent site of empty immigration kiosks and lines for foreigner nationals stretching far longer than those of Thais. Others say kiosks designed to hold two officers are often manned by one.

Some airlines expressed concern and confusion on Friday over an announcement a day earlier by Thailand's transport minister, Jarupong Ruangsuwan, to move flights to a different airport.

"We've never said we won't move but I'm asking for the government to be clear on this issue," Udom Tantiprasong, founder of local low-cost airline Orient Thai, told Reuters .

"If Don Muang is definitely going to be Bangkok's second airport for the foreseeable future, then we will begin our decision-making process but at the moment Orient Thai is waiting for clarification," he said.

"GOLDEN LAND"

Covering 3,200 hectares (7,900 acres), Suvarnabhumi and its two runways were the largest of its kind in Asia when they was unveiled, touted as Bangkok's answer to rival world-class airports in Singapore, Hong Kong and Kuala Lumpur.

Its construction was marred by graft scandals, delays and design problems. It was first proposed more than 40 years ago.

But even before it was christened in 2006, aviation experts predicted it would reach capacity in just a few short years. Some officials vowed the airport would be expanded to handle as many as 100 million passengers, but that never happened.

Suvarnabhumi, Thai for "golden land" and built on a swamp 25 km (15 miles) east of the sprawling capital, replaced the congested single runway of Don Muang, which re-opened a year later for domestic flights due to the capacity problems.

Low-cost carriers operating from Suvarnabhumi include Thai AirAsia, Nok Air and Orient Thai. Thai AirAsia is a joint venture between Malaysian low-cost airline AirAsia Bhd (AIRA.KL) and Thailand's Asia Aviation.

The Tourism Authority of Thailand expects 20.6 million tourists to visit Thailand this year, up 7 percent from 2011.

Mass-transit links between Suvarnabhumi, in the east of the city, and Don Muang to the north, are in their infancy, a likely inconvenience for travellers trying to connect between them.

(Editing by Jason Szep and Sanjeev Miglani)

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