* Air force chief says unidentified plane tracked 200 miles northwest of Penang
* Still no sign of missing plane, search in fifth day
* 227 passengers and 12 crew aboard lost flight
* Area being searched the size of Hungary
By Eveline Danubrata and Nguyen Phuong Linh
KUALA LUMPUR/PHU QUOC, Vietnam, March 13 (Reuters) - M alaysia's military has traced what could have been the jetliner missing for almost five days to an area south of the Thai holiday island of Phuket, hundreds of miles to the west of its last known position, the country's air force chief said on Wednesday.
His statement followed a series of conflicting accounts of the flight path of the Boeing 777-200ER with 239 people on board, which left authorities uncertain even which ocean to search in for Malaysia Airlines Flight MH370.
The last definitive sighting of the aircraft on civilian radar screens came shortly before 1:30 a.m. on Saturday, less than an hour after taking off from Kuala Lumpur, as it flew northeast across the mouth of the Gulf of Thailand bound for Beijing.
What happened next remains one of the most baffling mysteries in modern aviation history and the differing accounts put out by various Malaysian officials have drawn criticism of their handling of the crisis.
Rodzali Daud, the Malaysian air force chief, told a news conference on Wednesday that an aircraft was plotted on military radar at 2:15 a.m., 200 miles (320 km) northwest of Penang Island off Malaysia's west coast.
But there has been no confirmation that the unidentified plane was Flight MH370, Rodzali said, and Malaysia was sharing the data with international civilian and military authorities, including those from the United States.
"We are corroborating this," he added. "We are still working with the experts."
According to the data cited by Rodzali, if the radar had spotted the missing plane, the aircraft would have flown for 45 minutes and dropped only about 5,000 feet (1,500 metres) in altitude since its sighting on civilian radar in the Gulf of Thailand.
There was no word on which direction it was then headed, but if this sighting was correct, the plane would have turned sharply west from its original course, travelling hundreds of miles over the Malay Peninsula from the Gulf of Thailand to the Andaman Sea.
This would put it about 200 miles northwest of Penang, in the northern part of the Strait of Malacca, roughly south of Phuket and east of the tip of Indonesia's Aceh province and India's Nicobar island chain.
Indonesia and Thailand have said their militaries detected no sign of any unusual aircraft in their airspace. Malaysia has asked India for help in tracing the aircraft and New Delhi's coast guard planes have joined the search.
The U.S. National Transportation Safety Board said in a statement that its experts in air traffic control and radar who travelled to Kuala Lumpur over the weekend were giving the Malaysians technical help in the search.
A U.S. official in Washington said the experts were shown two sets of radar records, military and civilian, and they both appeared to show the plane turning to the west and across the Malay peninsula.
But the official stressed the records were raw data returns that were not definitive.
Authorities were continuing to search on both sides of the Malay peninsula in a total of over 27,000 square nautical miles (93,000 sq km), an area the size of Hungary or Indiana.
A dozen countries are taking part in the search, with 42 ships and 39 aircraft involved, Malaysian Transport Minister Hishammuddin Hussein said earlier on Wednesday.
There has been no sighting of any debris, prolonging the agonising wait for hundreds of relatives of those on board.
"My heart reaches out to the families of the passengers and crew," the minister said "And I give you my assurance we will not reduce the tempo and that we will not spare any effort to find the missing plane."
Malaysia has been criticised for giving conflicting and confusing information on the last known location of aircraft.
"The Malaysians deserve to be criticized - their handling of this has been atrocious," said Ernest Bower, a Southeast Asia specialist at the Center for Strategic and International Studies in Washington.
"They don't know where the plane is; they have briefed key partners and changed the story several times," he said.
The air force chief, in his remarks on Wednesday, denied saying a day earlier that military radar had tracked MH370 flying over the Strait of Malacca, saying that the radar sighting was still unconfirmed.
Amid the confusion, Vietnam briefly scaled down search operations in waters off its southern coast, saying it was receiving poor information from Malaysia. Hanoi later said the search was back on in full force and was even extending on to land.
"As long as the plane is not found, we would continue doing our mission," Vo Van Tuan, spokesman for Vietnam Search and Rescue Committee, told reporters in Hanoi.
China also said its air force would sweep areas in the sea, clarifying however that no searches over land were planned.
NOTHING RULED OUT
Authorities have not ruled out any possible cause for the plan's disappearance. Malaysian police have said they were investigating whether any passengers or crew on the plane had personal or psychological problems that might shed light on the mystery, along with the possibility of a hijacking, sabotage or mechanical failure.
The airline said it was taking seriously a report by a South African woman who said the co-pilot of the missing plane had invited her and a female companion to sit in the cockpit during a flight two years ago, in an apparent breach of security.
"We are shocked by these allegations. We have not been able to confirm the validity of the pictures and videos of the alleged incident," the airline said in a statement. The woman, Jonti Roos, has said she and a friend were invited to fly in the cockpit by Fariq between Phuket and Kuala Lumpur in 2011.
Hugh Dunleavy, the commercial director of Malaysia Airlines, told Reuters: "We have no reason to believe that there was anything, any actions, internally by the crew that caused the disappearance of this aircraft."
The Boeing 777 has one of the best safety records of any commercial aircraft in service. Its only previous fatal crash came on July 6 last year when Asiana Airlines Flight 214 struck a seawall with its undercarriage on landing in San Francisco, killing three people.
Boeing Co, the U.S. aircraft company that makes the 777, has declined to comment beyond a brief statement saying it was monitoring the situation.