U.S. civilian technicians spent about four hours aboard the Navy surveillance plane on China's Hainan Island on Wednesday to begin assessing the extent of damage, Pentagon officials said.

The technical experts from Lockheed Martin Corp., maker of the EP-3E Aries II aircraft, were allowed to board the plane at about 2 p.m. local time, officials said. They planned to return for a second day of work on Thursday.

On Tuesday, an American military spokesman in Hawaii said the United States still hopes that the aircraft damaged on April 1 in a collision with a Chinese fighter jet can be flown home. But officials at the Pentagon indicated that China had already made clear it would not allow the plane to be flown from the island.

Pentagon officials said they expected the spy plane would have to be at least partially disassembled and shipped off the island.

The Lockheed Martin contractors are assessing the extent of damage to the plane's engines and body to decide whether it can fly, Army Lt. Col. Stephen Barger, a spokesman for the U.S. Pacific Command, said Tuesday.

"That's the preferred way to get it out," Barger said by telephone from Hawaii. "Otherwise, it would have to be hauled out or possibly disassembled, which would take more time on the ground and would be more cumbersome."

The plane has been held at an air base on Hainan island in the South China Sea since making an emergency landing there after the April 1 collision over international waters.

Chinese authorities held the 24-member air crew for 11 days while demanding that Washington take the blame for the collision. The confrontation sent ties to their lowest point since U.S. warplanes bombed the Chinese Embassy in Yugoslavia two years ago.

The U.S. technicians arrived late Tuesday in Haikou, the capital of Hainan. Their inspection should take about two days, said Barger.

The technicians, who have refused to talk to reporters, spent Wednesday morning in the lobby coffee shop of a Haikou hotel, possibly waiting for a meeting with Chinese officials. Twenty to 30 Chinese agents in civilian clothes and military-style crewcuts sat in the lobby watching them.

On Tuesday, U.S. Ambassador Joseph Prueher said that the sooner the plane is returned to the United States, the sooner relations can mend.

"The airplane is sort of a corrosive element right now in our relationship. It's a reminder of a hard spot, and we need to clean that up and get on with things," said Prueher, who played a key role in winning the release of the U.S. crew.

The ambassador, who was ending his 17-month tour in Beijing, spoke to reporters at the Beijing airport before leaving for the United States.

Accounts from both sides indicate the plane lost its nose cone and damaged at least one of its four propeller engines in the collision. The impact pushed the U.S. plane into an 8,000-foot dive before the pilot regained control.

The Chinese F-8 fighter apparently broke in half, killing pilot Wang Wei. China has lionized the pilot, including this week's issuance of a commemorative envelope with a photo of Wang and his F-8 jet.

Vice President Dick Cheney said Sunday the U.S. plane cannot be flown now and will probably be taken out on a barge. The U.S. military will also consider using one of its mammoth C-5 or C-17 transport aircraft to carry the plane out.

U.S. officials said earlier that the Chinese apparently had ruled out allowing the plane to be repaired and flown out on its own.