And that is raising eyebrows.
Malaysia has insisted it has nothing to hide.
"If they say there's nothing to hide, then release this preliminary report, as virtually every other jurisdiction does with an accident," Thomas told CNN's Don Lemon.
The report was sent to the International Civil Aviation Organization, the U.N. body for global aviation.
"In most cases, the report is published because it's not a controversial document," CNN aviation correspondent Richard Quest said. "It's a statement of facts -- what happened. And if there are any controversial or difficult facts, they can be redacted."
The aviation organization did tell CNN about a safety recommendation in the report: Malaysia said the aviation world needs to look at real-time tracking of commercial aircraft.
It's the same recommendation that was made after the Air France Flight 447 disaster in 2009. But "nothing seems to have happened," Quest said.
"To suggest in the future that all planes worldwide are tracked in real time, one might suggest, is a pretty noncontroversial suggestion."
As an underwater drone keeps going up and back down, so do hopes that evidence from Malaysia Airlines Flight 370 has surfaced.
The metal object that washed ashore in Australia and sparked the curiosity of investigators Wednesday turned out to be unrelated.
And while the Bluefin-21 plunged into the Indian Ocean for its 12th mission Thursday, no one was certain the drone would find anything new.
"I think the chances are one out of 10," said Jules Jaffe, research oceanographer for the Marine Physical Laboratory.
The underwater probe has already scanned 90% of the designated search area, with no significant results.
Malaysian and Australian authorities are already mapping out a long-term strategy for the search, which could go on for months or years.
An expanded search area might include the last 370 miles of the plane's flight path, ocean search specialist Rob McCallum said.
"If the idea is to go more strategic and investigate the entire aircraft flight path, maybe 15 miles or so either side, then you need a more strategic tool, something like a deep-towed sonar that can provide a very large range indeed, at the expense of resolution."
The use of a deep-towed submersible device called the Orion is overdue, Thomas said.
"That should be brought in as quickly as possible, again, from the United States.
He said it may be time to go back and revisit the calculations of where the plane may be -- although officials have already been doing that.
"This is not an exact science," Thomas said. "We have to understand that."
Article By Holly Yan, CNN