Investigators began work to determine the cause of an airplane crash in Inner Mongolia Sunday that left 54 people dead. China Eastern flight MU5210 plunged into a frozen lake shortly after taking off from Baotou en route to Shanghai. All 47 passengers and six crew aboard were killed, as was one man on the ground, state media reported. The aircraft was a CRJ-200 built by Canada's Bombardier Aerospace. China Eastern has grounded all CRJs in its fleet, pending results of the investigation, Xinhua reported. An Indonesian passenger was the sole foreigner aboard, the airline said. The air crash is China's worst in more than two years. In May 2002, 112 people died when an MD-82 belonging to China Northern Airlines crashed into the ocean near the north-eastern city of Dalian.