Flt Lt Montri Chamriang, deputy director of the department, said the aircraft's flight data recorder revealed that the faulty bogie beam, which connects the wheels on an aircraft's landing gear horizontally, caused the plane's right landing gear to collapse on landing.
The plane, flight TG679 from Guangzhou, slid off the runway, injuring 40 passengers.
The accident may prompt THAI to shorten the interval between bogie beam replacements, he added.
He said bogie beams are meant to last no more than 50,000 take-offs and landings and have to be sent back to the Airbus headquarters in Toulouse, France, for major maintenance every 10 years.
The Airbus A330-300 aircraft had only made around 40,000 trips and the bogie beams were not due for maintenance until Dec 2014, he said.
The deputy director said the company will have to wait for Messier-Bugatti-Dowty, the landing gear manufacturer and the Airbus manufacturer to make an official announcement on the issue before the airline can proceed to making any changes.
THAI has 12 planes that use the same type of bogie beams, all of which are scheduled to be decommissioned in 2014 and 2015.
He said engineers have not started to fix the aircraft because they have to wait for the Aircraft Accident Investigation Committee of Thailand to produce a final report on the incident.
After receiving the report, the airline will have to set up a repair cost analysis committee and contact THAI's insurance company to conduct a full repair assessment, he said.
Flt Lt Montri said the repair cost is estimated to be no more than 21 million baht. If the plane is evaluated to have sustained more than 70% damage, the insurance company will compensate in full, he added.
He said that information obtained from the flight data recorder also assured that the accident was not caused by failure of other equipment, a hard landing or bad weather conditions.