By Jessie Yeung, CNN

(CNN) -- Australian investigators who led a four-year search for the missing Malaysia Airlines Flight 370 have defended their theory that the plane's disappearance was due to an accident.

Peter Foley and Greg Hood from the Australian Transport Safety Bureau told a parliamentary hearing Tuesday that the plane, which disappeared in 2014 carrying 239 people on a flight from Kuala Lumpur, Malaysia, to Beijing, had likely crashed into the Indian Ocean after running out of fuel.

The initial search, carried out by Malaysia, China and Australia, was called off in January 2017 after failing to find any trace of the plane within a 710,000-plus-square kilometer area of the Indian Ocean. A private company later took up the search.

The ATSB's investigation concluded that the pilot, Zaharie Ahmad Shah, was probably unconscious when the plane crashed. One of the plane's flaps was found in 2015 off the coast of Tanzania, suggesting they had not been deployed and that the plane was uncontrolled or barely controlled at the time of the crash.

Renewed speculation

Questions about the fate of MH370 were raised at an Australian Senate committee hearing following recent speculation that the plane's pilot had deliberately crashed the plane, killing everyone on board.

The flaps were an important discovery, Foley said at the hearing, because they "eliminated the potential for the actual aircraft to be controlled by an individual and be in a state where it was being control-ditched or likely to be."

Former Canadian air crash investigator Larry Vance told the Australian television program "60 Minutes" earlier this month that Zaharie had turned off the transponder and depressurized the plane, knocking passengers unconscious before crashing into the ocean.

Vance appeared on the program alongside a panel of aviation experts, including the former ATSB official in charge of the investigating the crash, a longtime Boeing 777 pilot and instructor, an oceanographer and others.

"He was killing himself," Vance said on the show, pointing to rumors of Zaharie's failing marriage as a possible motive. "Unfortunately, he was killing everyone else on board. And he did it deliberately." Vance has written a book about the plane's disappearance.

Foley acknowledged that the ATSB had consulted experts who believed in the "controlled ditching" theory, and he said that it was "not impossible, but unlikely."

He pointed to holes in Vance's theory: For one, Zaharie would have suffered from decompression sickness as well and would have likely been unable to pilot the plane. Previous evidence further suggests the plane spiraled fast into the ocean instead of making a controlled descent.

"We considered every piece of evidence at the time in an unbiased fashion, and what we are seeing in the press is perhaps a lot of speculation about a single piece of evidence," Foley said.

"I would like to re-characterize it as not a ghost flight, not a death dive."

Richard Quest, CNN's aviation correspondent and author of "The Vanishing of Flight MH370," has also dismissed the rogue pilot theory, noting that pilot suicide is rare and that there is no evidence to make a case against the captain.

"This theory that the captain did it has been around since day one, and this program didn't really advance the argument as to the evidence that proves it," Quest said last week.

"I promise you there is not a single shred of new evidence as to what happened to that plane. There is lots of extrapolation. There is lots of conclusions and people thinking if you take one and one, it must equal two," Quest added. "But was it nefarious? Was it mechanical? Was it something else? We still do not know."

Zaharie's sister, Sakinab Shah, told CNN in 2016 that any suggestion that her brother deliberately brought down the plane was a "fabrication."

"He's been made a scapegoat from the beginning," Shah said.