(Bloomberg) -- Pilots of a doomed China Eastern Airlines Corp. flight failed to respond to multiple calls from air-traffic controllers after tipping into a deadly nosedive, authorities said after the first full day of searching through the wreckage.

Investigators offered no major insights as to why a Boeing Co. 737-800 jet carrying 132 people crashed in southern China, saying at a press conference late Tuesday that it was too early draw any clear judgments about the cause.

Rough terrain and the state of the aircraft, which plunged rapidly from about 29,000 feet (8,840 meters) into a hillside, make the search difficult. The black boxes from Flight 5735 haven’t been recovered, Zhu Tao, an official with the Civil Aviation Administration, said at the briefing.

China Eastern grounded its fleet of 737-800s and thousands of domestic flights were canceled Tuesday across the nation. Chinese officials ordered a sweeping two-week safety review after the jet crashed near Wuzhou in the Guangxi region. All 123 passengers and nine crew are presumed dead.

Key Developments:

  • Pilots didn’t answer calls; no black box found
  • Airline says pilots, plane were fit before flight
  • Chinese regulator orders sweeping air-safety review
  • Aircraft’s nosedive from 29,000 feet puzzles experts

No Response (9:54 p.m. HK)

Air traffic controllers tried multiple times to reach pilots of doomed China Eastern Flight 5735 after it tipped into a deadly dive on Monday but received no response to their calls, an official with China’s Civil Aviation Administration said at a press briefing. 

The plane disappeared from radar screens at 2:23 p.m. local time, three minutes after it started a steep descent, the official, Zhu Tao, said at the end of the first full day of searching through the wreckage. No survivors have been found.

Based on current information, Chinese officials are unable to make clear judgment about the cause of Monday’s crash, Zhu said. The ongoing investigation will be difficult, he said, describing a devastating impact and hilly terrain in the search area. 

The so-called black boxes -- separate voice and data recorders which are actually orange in color -- haven’t yet been found, state-backed news agency Xinhua reported. The team will continue to collect evidence toward a full understanding of the cause, Zhu said. 

Plane, Pilots Fit (9:54 p.m. HK)

The Boeing jet met airworthiness standards before taking off, and technical conditions were stable, Sun Shiying, a China Eastern official, said at Tuesday night’s briefing, according to the South China Morning Post. The nine crew mambers were experienced and in good health, he said, according to the newspaper. 

Rough Terrain (9:54 p.m. HK)

Video footage showed dozens of rescue workers, some in military uniforms, using shovels to dig through  hillside littered with debris. They found wallets and bank cards belonging to some of the passengers, China state television reported. 

Air-Safety Review (8:48 p.m. HK)

The Civil Aviation Administration of China ordered a sweeping two-week safety assessment that encompasses air-traffic control bureaus, airlines, airports and flight-training organizations, according to the agency’s CAAC News, which cited an official notice. 

At the same time, China Eastern is beefing up cockpit crew requirements on at least some aircraft types. Two senior captains, with an instructor in the lead, and one senior co-pilot are now required for safety redundancy, The Paper reported. Alternatively, two flight instructors, one being the captain, can work with a senior co-pilot, the Chinese news outlet said, citing people who worked at China Eastern. 

The Sun reported earlier that the crew involved in Monday’s crash included a pilot, a co-pilot and a trainee pilot in the jumpseat. The U.K. newspaper cited unnamed sources in China. 

Bad Weather May Hamper Recovery Efforts (3:22 p.m. HK)

Torrential rain is forecast in the crash area, which may impede rescue efforts, Xinhua News Agency reported. High winds are also expected. Caixin said weather conditions were good at the time of the crash, citing an official from China’s meteorological administration.

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