That's the big question on the mind of Indonesia's Transportation Minister as investigators finish preparing the initial report into the crash last month of the Airbus A320-200 with 162 passengers on board.
"The question is why this plane suddenly climbed" from 32,000 feet to almost 38,000 feet "without any information and any warning," Ignasius Jonan told CNN in an interview Monday.
Jonan said none of the other planes in the area experienced the turbulent weather patterns that led the pilot of QZ8501 to request a change of course and an increase in altitude shortly before it disappeared off radar.
Data provided by the Indonesian Transportation Ministry shows that less than three minutes after making that request, Flight QZ8501 began climbing sharply, rising nearly 6,000 feet in less than a minute.
The plane then fell rapidly and disappeared off radar in the middle of the Java Sea. That sequence of events is based on radar and transponder information, not on the contents of the plane's flight data recorder.
No plans to make initial report public
The analysis of the information from the data recorder, and the other so-called black box, the cockpit voice recorder, is expected to be part of the preliminary report that Indonesia is due to submit to international air safety regulators by January 28.
The Transportation Minister told CNN that he wants to ensure the victims' families and the public are kept informed and that there's nothing hidden from them.
But when asked if that meant he would release the preliminary report to the public, he said no.
Jonan said he will urge investigators to release the final report as soon as possible.
"It won't be a year, that's my promise," he said.
Jonan oversaw an investigation into why Flight QZ8501 was able to take off on a Sunday, even though AirAsia lacked permission to fly from Surabaya to Singapore on that day of the week.
His inquiry discovered 60 other flights had been running without proper approvals. Those flights have been banned, he says, and ministry officials are now regularly checking the schedules.
While he calls the issue of flights operating without permission a "big worry," he says he believes it was unrelated to the crash of Flight QZ8501.
He also says he thinks that this crash should not be seen as a permanent black mark against Indonesia's safety record.
"We run around 1,000 flights a day and 7000 flights a week," Jonan said. "And that's a lot of flights in the air of Indonesia. So one crashed unfortunately. So I would suggest it's not a big issue that can make everybody not fly in the air of Indonesia."