By David Shepardson (Reuters) -The U.S. National Transportation Safety Board (NTSB) said Friday it was assisting Chinese investigators with the download of the cockpit voice recorder in Washington from an China Eastern Airlines Boeing 737-800 jet as it sent a team of investigators to China. The U.S. safety board told Reuters it was helping the Civil Aviation Administration of China “with the download of the cockpit voice recorder from China Eastern Flight 5735 in our lab in Washington.” China’s decision to send a key piece of evidence to Washington for assistance shows the urgency of the inves…