Part of the landing gear had also been subject to an aviation watchdog warning.
A THAI A330-300 veered off the runway after landing at Suvarnabhumi airport on Sunday, injuring 40 people.
THAI executive vice-president for the technical department, Flt Lt Montree Jumrieng, said Wednesday that preliminary testing showed the accident was the result of a defective bogie beam on the aircraft's landing gear. He said the faulty part caused the gear to collapse about 1km down the runway.
A bogie beam connects the wheels on an aircraft's landing gear horizontally and allows them to pivot on takeoff and landing.
According to Flt Lt Montree, Airbus recommended close surveillance of the bogie beams of its A330-300 planes when THAI ordered them. The landing gear was manufactured by French-based firm Messier-Bugatti-Dowty Co.
The European Aviation Safety Authority (EASA) issued an emergency airworthiness directive on June 29, 2011, about the landing gear of some Airbus aircraft series, including the A330-300.
The directive said during ground load test cycles, the main landing gear (MLG) bogie beam prematurely fractured as a result of its assembly method.
"Fracture of a MLG bogie beam under high speed could ultimately result in the aeroplane departing the runway, or in the bogie detaching from the aeroplane, or MLG collapse, which could cause structural damage to the aeroplane and injury to the occupants," the directive read.
EASA ordered a reduction in the existing MLG bogie beam life cycle.
"The bogie beam has a life span of 10 years and [the one which broke on Sunday] had not been replaced since it was first installed [in 2004]. But I can confirm that it was checked every two years," Flt Lt Montree said.
He said that due to the warning from Airbus, THAI checked the landing gear every two years and Airbus staff always took part in the inspections.
"We found[cracks on the bogie beams] on some of our A330-300 aircraft after three to four rounds of maintenance.
The affected parts were replaced," he said, stressing that THAI adheres strictly to maintenance regulations.
He said the airline operates 27 Airbus A330-300 aircraft. The plane involved in Sunday's accident was delivered in 1995 and was among the first batch of 12 A330-300s that THAI purchased.
This group of aircraft is due to be decommissioned between next year and 2017.
The bogie beam involved in Sunday's accident was last checked in February last year, when it was found to be in a usable condition, Flt Lt Montree said.
He added that the plane involved in the accident would require two new engines and three new bogie beams.
THAI senior executive vice-president Chokchai Panyayong said the landing accident had caused serious damage to the aircraft.
The plane was removed from Suvarnabhumi's eastern runway about 3.30pm Wednesday, and the runway was reopened at 8.10pm.
THAI president Sorajak Kasemsuvan had conducted a ceremony to pray for the smooth removal of the plane Wednesday morning after heavy rain delayed salvage efforts on Tuesday night.
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