The aviation industry is calling for a ban on new flights operating through Suvarnabhumi airport to prevent further congestion.
The Airline Operators Committee (AOC), a coalition of 86 international airlines and 26 aviation service providers operating at Suvarnabhumi, is urging authorities to impose the ban immediately.
"Authorities should come to their senses and realise Suvarnabhumi can no longer accommodate more flights beyond the current level. We know it's a painful decision," AOC chairman Louis Moser told the Bangkok Post.
Overcrowding has become a critical problem at the airport, one that will become worse as the six-month "winter programme" begins in the final week of this month. Airport use is expected to rise by 10% during this period.
Suvarnabhumi has been operating beyond its design capacity of 45 million passengers annually for several years.
According to figures released last week by Airports of Thailand Plc (AoT), passengers passing through the airport set a new record of 52.4 million in fiscal 2015, which ended on Sept 30, up by 12.7% year-on-year and exceeding capacity by 17%.
If AoT's 9.7% growth projection in passenger throughput at Suvarnabhumi in the calendar year 2016 is realised, the numbers will reach 70.9 million, making the congestion unbearable, Mr Moser said.
Based on their experience, AOC members say they have exhausted the means to squeeze in more capacity, he said.
"Better slot management, double aircraft parking -- you name it, they've done it," Mr Moser said.
"It's very stressful to ensure smooth, safe and sound services in such a hostile environment."
Banning newcomers and discouraging existing operators from adding more flights seems to be the only solution before Suvarnabhumi adds additional capacity through its Phase 2, which is more than five years away.
Capping flights through Suvarnabhumi has needed to be addressed for quite a while, but no authorities would dare talk about the issue in recent years, Mr Moser said.
However, former transport minister Prajin Juntong, now a deputy prime minister, in May suggested the country could restrict flights, saying rapid growth risked dangerously overloading the airspace as well as airport capacity.
ACM Prajin linked the restrictions to Thailand's "open sky" policy, which then was under review in an effort to maintain aviation safety.
He told reporters Thailand must start what he termed an "open sky with conditions policy".
The retired ACM was quoted as saying, "There's not enough airspace to serve more flights. We need to think more seriously about safety and prevent possible aeroplane crashes."
He did not name the airports that were subject to the restrictions, but industry executives agreed he was referring to Suvarnabhumi, which handles the bulk of Thailand's air traffic.
AoT, the state-controlled firm that runs the country's six main airports including Suvarnabhumi, discounted the industry's suggestions that congestion at Thailand's air gateway had gotten out of hand.
While he agreed the airport was busy, AoT president Nitinai Sirismatthakarn told the Bangkok Post the 45-million-passenger-a-year capacity was only a reference figure.
The figure is based on the assumption that the airport runs at full capacity of 11,000 passengers an hour for three hours a day, with the remaining 21 hours handling 4,400 passengers an hour, he said.
"So in theory, Suvarnabhumi can accommodate up to 300 million passengers a year if pushed to the limit," Mr Nitinai said.
He said there had been too much concern about congestion and urged concerned parties to come up with specific areas where the issue needed to be addressed.
The surging traffic through Suvarnabhumi is manageable, and AoT has been proactive in resolving any problems that crop up, Mr Nitinai added.