* Second advanced U.S. P8 Poseidon to join Indian Ocean hunt
* Search flights resume after treacherous weather eases
* Thai, Japanese satellites spot many more objects
* Search area covers some of world's roughest seas
By Matt Siegel and Michael Martina
PERTH, March 28 (Reuters) - An air search of the remote southern Indian Ocean resumed on Friday, seeking to confirm if hundreds of objects spotted by satellites are debris from a Malaysian jetliner presumed to have crashed almost three weeks ago with the loss of all on board.
A Chinese Ilyushin IL-76 took off from Perth before dawn, heading 2,500 km (1,550 miles) southwest into the search area where high winds and icy weather had halted flights on Thursday.
The disappearance of the Malaysia Airlines jet, which vanished from civilian radar screens less than an hour after taking off from Kuala Lumpur on a routine flight to Beijing on March 8, has gripped the world and baffled investigators.
Officials believe someone on board Flight MH370 may have shut off the plane's communications systems before flying it thousands of miles off course where it crashed into the ocean in one of the most isolated and foreboding regions on the planet.
Theories range from a hijacking to sabotage or a possible suicide by one of the pilots, but investigators have not ruled out technical problems.
The search zone centres on the latest sightings of possible wreckage that were captured by Thai and Japanese satellites in roughly the same frigid expanse of sea as earlier images reported by France, Australia and China.
"We detected floating objects, perhaps more than 300," Anond Snidvongs, the head of Thailand's space technology development agency, told Reuters. "We have never said that the pieces are part of MH370 but have so far identified them only as floating objects."
The U.S. Navy said it was sending a second P8 Poseidon maritime surveillance aircraft to help in the search for the missing Boeing 777.
"It's critical to continue searching for debris so we can reverse-forecast the wind, current and sea state since March 8th to recreate the position where MH370 possibly went into the water," said Commander Tom Moneymaker, a U.S. 7th Fleet oceanographer.
The United States has also sent a device that can be towed behind a ship to pick up faint pings from the plane's black box voice and data recorders, but time is running out.
"We've got to get this initial position right prior to deploying the Towed Pinger Locator since the MH370's black box has a limited battery life and we can't afford to lose time searching in the wrong area," Moneymaker said.
The Australian Maritime Safety Authority, which is coordinating the effort, said it would give details later on the search after flights were halted on Thursday.
"It's the nature of search and rescue. It's a fickle beast," Flying Officer Peter Moore, the captain of an Australian AP-3C Orion, told Reuters aboard the plane after it turned around 1,000 km (600 miles) from the search zone.
"This is incredibly important to us. The reality is we have 239 people whose families want some information and closure."
The objects spotted by the Thai satellite on Monday were between 2 metres (6.5 ft) and 16 metres (52 ft) in size and were in an area around 2,700 km (1,680 miles) southwest of Perth, Snidvongs said.
The prolonged and so far fruitless search and investigation have taken a toll, with dozens of distraught relatives of 150 Chinese passengers clashing with police and accusing Malaysia of "delays and deception".
China has repeatedly voiced its frustration with the efforts of Malaysia to find the plane. China's special envoy to Malaysia said on Thursday that Beijing was doing its best to push the Southeast Asian nation to coordinate the international search effort, state news agency Xinhua said.
Chinese insurance companies have started paying compensation to the families of passengers, Xinhua reported separately.
A U.S.-based law firm has said it expects to represent families of more than half of the passengers in a lawsuit against the carrier and Boeing, alleging the plane had crashed due to mechanical failure.
(Additional reporting by Suilee Wee in Beijing, Niluksi Koswanage in Kuala Lumpur, Stanley White in Tokyo and Amy Sawitta Lefevre in Bangkok; Writing by Lincoln Feast and Alex Richardson; Editing by Dean Yates)