The officials summoned reporters Thursday to clarify comments made at a news conference the day before, where some media reported the investigators had said the plane was not airworthy when it took off.
The issue of airworthiness is crucial because of concerns over technical issues with the new Boeing 737 MAX that crashed and questions over the airline's safety procedures.
All 189 people aboard the flight between Jakarta and a regional airport died in the disaster.
The National Transportation Safety Commission investigators were reporting this week on data from the aircraft's black boxes. They say the cockpit voice recorder, which is still missing and being searched for, is needed to understand what exactly caused the jet to plunge in the Java Sea just 11 minutes after takeoff.
On Wednesday, Utomo said the plane had experienced technical problems on four of the six flights before it crashed. On its penultimate flight, as during the final one, pilots struggled to prevent an automatic safety feature from forcing the nose of the aircraft down due to problems with its sensors.
Utomo said that based on maintenance records, flight engineers had made repairs and run tests.
"Based on the test results, the aircraft was declared airworthy, also when the plane departed from Jakarta, the aircraft was in airworthy condition," he said.
Another investigator, Ony Suryo Wibowo, said there were special procedures to be followed when there are problems with an aircraft.
"But in principle, when the engineer has stated it's airworthy, then it's airworthy," he said.
Wibowo said the pilot would make the final choice about whether or not to cancel or abort a flight, and the investigators were trying to understand how the pilot made his decision "When the plane is on the ground, the responsibility for airworthiness is on the engineer, and when the plane is in the air, the airworthiness is entirely in the pilot's hands," he said.
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