TRANSPORTATION

NTSB Recommends Grounding Two Types of Helicopters: The National Transportation Safety Board said in a letter that it was recommending the action until experts can figure out what caused four crashes that killed seven people in Germany, Switzerland and the United States last year. In each case, investigators suspect malfunctioning rotor blades on the light helicopters Robinson R-22 and Robinson R-44, manufactured by the Robinson Helicopter Co. of Torrance. In at least three cases, the blades hit the main bodies of the helicopters or sliced off their tails, the board told the Federal Aviation Administration in the letter, which was delivered Thursday. “The safety board is specifically concerned that the unique design of the R-22 and R-44 rotor system may result in flight characteristics that are not adequately addressed by” certification testing, the letter said. Frank Robinson, president of the helicopter manufacturer, called the safety board’s recommendation “completely uncalled-for. The accident rate of the R-22 is the lowest it’s ever been. It’s gone continually down through better training and better education of pilots.”