Dr Narupol Chaiyut, a member of a committee overseeing service problems at the new airport, estimated that 70 percent of the problems would be fixed in 2007. Twenty of the 60 problems were successfully fixed by February 2007. Suvarnabhumi Airport's main terminal roof is designed with structural elements and bays placed in a cantilevered, wavelike form to appear to "float" over the concourse beneath. This overall design principle was to express the former essence of the site, from which water had to be drained before construction could begin. The eight composite 2,710-ton trusses supporting the canopy of the main terminal are essentially diagrams of the bending moments acting on them, with the greatest depth at mid-span and over the supports. The result of Helmut Jahn's vision is a structure with performance materials serve in their total composition and in use more than in their conventional roles. This maximizes daylight use in comfort with substantial energy life-cycle cost savings. The installed cooling system reduced up to 50 percent compared to a conventional system. A translucent membrane with three layers was developed to mediate between the interior and exterior climate, dealing with noise and temperature transmission, while still allowing natural flow of daylight into building. The airport was ranked number 48 among the world's top 100 airports in 2020. Other ASEAN airports in 2020 were ranked: Singapore Changi Airport, 1; Kuala Lumpur International Airport, 63; Jakarta, 35; Hanoi, 87. Suvarnabhumi was ranked 46 in 2019, 38 in 2017 and 36 in 2016. According to the Thailand Development Research Institute (TDRI) in 2018, the airport's ranking had not improved over the past six years. Customer complaints include: lengthy immigration waiting times; transit day room issues; insufficient numbers of chairs and phone charging points; insufficient English-speaking staff; and poor information displays. On 25 January 2007, due to work upgrading the taxiways which suffered from small cracks, a few incoming flights were delayed and several flights were safely diverted to U-Tapao International Airport in Rayong Province. On 26 November 2008, an illegal occupation of the airport took place by People's Alliance for Democracy, closing the departure lounge and blocking exits and leaving almost 3,000 passengers stranded in the main terminal and another 350,000 stranded inside the country, as all flights were grounded. The People's Alliance for Democracy seized the control tower at 12:00. On 2 December 2008, protesters agreed to leave the airport as they had been illegally protesting and permitted the resumption of flights.