"Based on the coordinates given to us and evaluation that the estimated crash position is in the sea, the hypothesis is (that) the plane is at the bottom of the sea," National Search and Rescue Agency chief Bambang Soelistyo told reporters in Jakarta.
"That's the preliminary suspicion and it can develop based on the evaluation of the result of our search," he said.
If the plane is found on the ocean floor, there would be a challenge in getting the plane to the surface because they do not have the "submersible" equipment, Soelistyo said.
Searching for the Singapore-bound Flight QZ8501, an Indonesian helicopter today saw two oily spots in the Java Sea while an Australian search plane spotted "suspicious" objects near Nangka island, more than 1000 km from the location where contact with the plane was lost.
However, Indonesian Vice President Jusuf Kalla said the objects spotted by the Australian aircraft were not from the missing plane. "It has been checked and no sufficient evidence was found to confirm what was reported," Kalla told reporters at Surabaya airport from where the plane took off.

Indonesia Air Force spokesman Rear Marshal Hadi Tjahnanto told MetroTV that an Indonesian helicopter spotted two oily spots in the Java Sea east of Belitung island, but there was no confirmation that the finding had a connection with the missing plane.
Tjahnanto said the search was now focussed on the oil spots.
The Vice President stressed that there was no time frame for the search mission and anything found will be treated with utmost importance.
"Indonesia hopes there will be survivors but is prepared for the worst," Kalla said.
The Airbus A320-200 lost contact with air-traffic control less than an hour after takeoff yesterday. Contact with the plane was lost shortly after a request was made by the pilots to climb to a higher altitude to avoid bad weather.
The last communication from the pilot to radar control was a request to increase altitude from 32,000 feet to 38,000 feet because of rough weather.
The request was not immediately granted as there was reportedly another plane in airspace at 34,000 feet, said Bambang Tjahjono, director of the state-owned company in charge of air-traffic control.
AirAsia Flight QZ8501 was carrying 155 passengers – one British, one Malaysian, one Singaporean, three South Koreans, 149 Indonesians -- and seven crew members -- six Indonesians and a French co-pilot.

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