US probes plane that violated White House airspace Tuesday April 2, 7:07 PM EST WASHINGTON, April 2 (Reuters) - Frontier Airlines (FRNT) grounded two pilots at the controls of a jetliner that flew virtually over the White House in violation of security regulations heightened after the Sept. 11 attack on Washington, officials said on Tuesday. The incident occurred late on Monday as the Boeing (BA) 737-300 was taking off from Washington's Ronald Reagan National Airport, just across the Potomac River from the executive mansion and other U.S. landmarks. The plane failed to make the required turn away from the White House as it made its steep climb, Federal Aviation Administration officials said. Air traffic controllers notified the crew that the plane, on a regularly scheduled flight to Denver, had violated White House airspace and the plane then changed course. An aviation official said the aircraft flew almost directly over the White House grounds. President George W. Bush was there at the time. The Secret Service met the plane in Denver and questioned the crew. A spokeswoman for the Denver-based airline, Tracey Kelly, said the pilots had been grounded by the carrier until federal and company investigations were completed. "We're working with the FAA and the TSA (Transportation Security Administration) to determine what happened and make sure it does not happen again," Kelly said. There have long been airspace restrictions over the White House, but air security in and around Washington has been tightened considerably since the Sept. 11 hijack attacks. White House security officials were reluctant to open Reagan National after the terrorist attacks on the World Trade Center and the Pentagon, and have only permitted service to return gradually to the airport. ©2002 Reuters Limited.