PORTLAND – Activity at the Portland International Jetport came to a halt for about a half-hour late Tuesday morning when a contractor’s backhoe ruptured a natural gas line near the control tower. The control tower was evacuated, flights were put on hold, and passengers were confined to the terminal until a crew from Northern Utilities could arrive and shut off the line. Jetport manager Jeff Schultes said few flights were affected because the accident occurred after most of the morning’s arrivals and departures.