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Emergency workers using sniff dogs to conduct search for the black box near the debris at the China Eastern flight crash site in Tengxian County in southern China's Guangxi Zhuang Autonomous Region. Image Credit: AP

WUZHOU, China: The search area was expanded Thursday for the second black box from a China Eastern passenger jet that crashed in southern China with 132 people on board earlier this week, state broadcaster CCTV said.

Off-and-on rain was impeding the search for a second straight day. One of the black boxes was found Wednesday. Its outer casing was damaged but the orange cylinder was relatively intact, investigators said.

Three days after the crash, officials said they had found 183 pieces of the plane including engine parts and cockpit items, 21 objects belonging to victims and some human remains. State broadcaster CCTV showed footage of workers on a denuded slope trying to dislodge a white wing section with the red and blue China Eastern logo on it.

Pumps were being used to drain a water pond as an off-and-on light rain hampered the search effort for a second straight day. More than 300 searchers were taking part, said Huang Shangwu, a deputy chief in the Guangxi Fire and Rescue Department.

"The water pumping yesterday greatly contributed to the finding of the black box,'' Huang told reporters at a command center inside a wide restricted zone that has been blocked off by authorities.

The Boeing 737-800 was cruising at 29,000 feet (8,800 meters) when it suddenly nose-dived into a remote mountainous area on Monday, setting off a fire in the surrounding forest that could be seen in NASA satellite images. No survivors have been found.

The Boeing 737-800 was cruising at 29,000 feet (8,800 meters) when it suddenly nose-dived into a remote mountainous area on Monday, setting off a fire in the surrounding forest that could be seen in NASA satellite images. No survivors have been found.

A first black box found on Wednesday was the cockpit voice recorder based on an early assessment, a Civil Aviation Administration of China (CAAC) official told reporters.

The recording material appeared to have survived the impact in relatively good shape, and was being sent to Beijing for analysis, the official said.

The cockpit voice recorder would provide investigators with details of the communications between the flight’s three pilots, which is one more than is normally required on board a Boeing 737-800 plane.

Flight MU5735 was en route from the southwestern city of Kunming to Guangzhou on the coast on Monday when the plane suddenly plunged from cruising altitude at about the time when it should have started its descent before landing.

According to flight tracking website FlightRadar24, the plane briefly appeared to pull out of its nosedive, before plunging again into a heavily forested slope in the mountainous Guangxi region of southern China.

Chinese authorities said the pilots did not respond to repeated calls from air traffic controllers during the rapid descent.

Searchers have been using hand tools, metal detectors, drones and sniffer dogs to comb the heavily forested and steep slopes. Wallets, identity and bank cards and human remains have been found.

CCTV news showed police in olive- and dark-coloured rain gear standing in a cleared area on Thursday, some with bare or white-gloved hands atop long-handled tools that appear to be shovels or sickles. They all wore surgical masks.

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Search underway. Image Credit: Reuters

Recovering the so-called black boxes — they are usually painted orange for visibility — is considered key to figuring out what caused the crash.

Cockpit voice recorders can capture voices, audio alerts and background sounds from the engine or even switches being moved. The flight data recorder stores information about the plane’s airspeed, altitude and direction up or down, as well as pilot actions and the performance of important systems.

Investigators have said it is too early to speculate on the cause. An air-traffic controller tried to contact the pilots several times after seeing the plane’s altitude drop sharply, but got no reply, officials have said.

The China Eastern flight was headed from Kunming, the capital of Yunnan province, to Guangzhou, a major city and export manufacturing hub on China’s southeastern coast. China Eastern, headquartered in Shanghai, is one of China’s four major airlines.

THERMAL CAMERAS AND DRONES

Mist and low lying clouds hovered over the small, tree-covered hills in the mainly rural area surrounding the crash site on Thursday, where state media reported part of one of the plane’s engines was recovered.

Search teams combed ground vegetation and soil with sticks and even their bare hands on the rain-sodden slopes, according to state television. Some of them also carried thermal cameras to detect signs of life.

Drones were readied for deployment to survey the core area of the crash site and capture images to be assessed by experts, state media said. Other drones that can be airborne for more than 12 hours will be deployed to provide night-time light.

The crash investigation is being led by China but the United States was invited to take part because the plane was designed and manufactured there.

The U.S. National Transportation Safety Board said on Wednesday it had not yet determined if investigators would travel to China in light of strict visa and quarantine requirements.