U-Tapao is 115 kilometres (about 70 miles) from Suvarnabhumi airport.
Mr Chadchart said that the UPS supplying electricity for the radar system experienced problem on Thursday evening, and the back-up power supply was not working. Engineers took around 40 minutes to repair.
During the time that there was no radar system functioning, some flights were waiting, queuing to land at Suvarnabhumi airport, but six flights were running out of fuel and opted to land at U-Tapao without any safety problems.
The aircraft re-fueled at U-Tapao before returning to land at Suvarnabhumi Airport.
He said that radar at Don Mueang airport was also not working given that it was under the single aircraft navigation system covering both Don Mueang and Suvarnabhumi. Each airport facilitates incoming flights with its own control tower's navigation system only when aircraft enter a 10km radius of the airport.
A back-up radar system that could cover both airports together is at Thung Maha Mek and could operate effectively, but there was no staff manning the system at the time when it was needed, when there was power supply problem.
Mr Chadchart said the incident caused delays of 40 minutes for incoming flights while the longest delay for departing flights was three hours.