The National Highway Traffic Safety Administration (NHTSA) has launched an investigation into General Motors 2006 medium duty commercial trucks which include the Chevrolet Kodiak W4500 and W5500, GMC TopKick C4500 and C5500 and Isuzu 4500 and 5000 Series. There have been no injuries to date, but several complaints of fan blades separating from the vehicle have been reported. The problem is being blamed on flexible fan blades that may develop cracks over time. If the investigation should lead to a recall, almost 60,000 medium duty trucks could be affected.