Despite a huge international search operation involving nearly 100 aircraft and ships, four days on, there have been no sightings of ill-fated Malaysia Airlines flight MH370.

A large expanse of litter-strewn sea and a “bewildering” lack of information about the last moments in the cockpit have confounded search and rescue efforts.

“Based on our assessment so far, there is little hope for a good outcome for the missing Malaysian plane,” deputy chairperson of Vietnam’s National Search and Rescue Committee, Pham Quy Tieu, said.

“The biggest challenges right now is time, the more time passes, the less chance we have to save lives,” said Bleu Moore, spokesperson from the United States 7th Fleet public affairs office.

Experts have speculated about why dozens of ships and aircraft carrying state-of-the-art technology haven’t seen any sign of the plane.

Part of the problem is the amount of rubbish floating in the sea, said Greg Waldron, Asia managing editor of Flightglobal , a trade publication for the aviation sector.

Objects as small as styrofoam balls used for fishing nets can make detecting significant objects harder, he said.

“Radar is actually designed to filter these kinds of things out because it’s too cluttered a picture - so what happens is, if you turn off that software, suddenly you see a million different things so

there are all these potential contacts out there that you can’t possibly investigate.”

Infra-red sensors, which detect heat variations, are also of limited use as debris floating on the sea tends to be the same temperature as the water.

“That means the aeroplanes involved in the search are very much restricted to using the naked eye: men and women looking out of the window with binoculars to find things,” Waldron said.

“Even though it’s a very large aircraft, relative to the size of the sea it’s a very small space, so it’s like looking for a needle in a haystack.”

Reports have compared the jet’s disappearance to Air France flight AF447, which crashed in the South Atlantic in 2009. It was several days before pieces of the wreckage were identified and some pieces had drifted for hundreds of kilometres from the scene of the crash.

It took investigators nearly two years before the ‘black box’ data recorder was recovered and the reason for the crash determined.

Key is finding wreckage

The key to finding the plane is finding pieces of the wreckage, Waldron said. Once these have been identified, experts can study the currents and start working out where the plane actually impacted the water, he said.

Then the focus is on finding the flight data recorder and cockpit voice recorder, which have the power to transmit their location for about a month, he said.

“You’re looking for one thread that can lead you to this journey of discovery,” Waldron said. “They haven’t found anything yet; it’s going to be a long, tough search.”

US Navy spokesperson Cooper said he did not know how long the Malaysian authorities would maintain hope that anyone on the plane would still be found alive.

“I’m not sure how long they can hold on, but we’ll search the area until it’s called off,” he said.

- dpa