Even as fighter jets were scrambled on successive days this month to intercept airspace violators near the presidential retreat at Camp David, Md., military and civilian aviation officials say fewer pilots are breaking U.S. airspace restrictions this year.
The Aircraft Owners and Pilots Association, which represents private and business pilots, has been trying to reduce the number of airspace violations through publicity and training, said Craig Spence, the organization's vice president for operations and international affairs.
The group is also working with the Federal Aviation Administration to configure airspace restrictions to minimize disruption of private flights but still protect people on the ground, Spence said.
"We have one common goal, and that's making sure there are no (temporary flight restriction) violations," he said.
Nationwide, the number of airspace violations is down so far this year, according to FAA figures.
The FAA has reported 122 airspace violations in 2011, a pace that would result in about 220 for the full year. That would be the lowest by far since 2008, when the agency began tracking the number in detail.
The FAA reported 387 violations in 2008, 358 in 2009 and 382 in 2010.
The North American Aerospace Defense Command scrambled fighter jets twice on July 9 and once on July 10 to intercept private planes that were flying near Camp David and weren't in radio contact with civil aviation officials. President Barack Obama was at Camp David for part of that weekend.
All three planes left the restricted area and landed at nearby airports. An FAA spokesman said he didn't know whether any of the pilots faced civil or criminal action.
Since the Sept. 11, 2001, terrorist attacks, NORAD aircraft have responded to 3,432 airspace violations nationwide, or about 346 a year, said NORAD spokesman Lt. Mike Humphreys. NORAD aircraft actually intercepted violators an average of 140 times a year, he said. In the other cases, the planes left restricted areas before the interceptors arrived.
"It's more often ... that we scramble and don't intercept than we scramble and do intercept," Humphreys said. NORAD sends aircraft only if the FAA requests it.
The FAA can impose a range of airspace restrictions. Some highly sensitive areas, including Camp David and Washington, D.C., are always off-limits. Other places are designated air defense identification zones, where pilots are required to identify themselves to air traffic controllers.
The FAA also can impose temporary flight restrictions when the president or other dignitaries are in an area, or for special situations such as space launches, air shows, big sporting events or disasters.
Restrictions apply primarily to general aviation flights, which include private pilots and business flights but not scheduled commercial flights or military aircraft.
NORAD doesn't calculate the price tag of each incident, but the aircraft most commonly used to respond cost between $7,800 and $19,600 per hour to fly, according to military calculations, including the U.S. Coast Guard. Those aircraft include the Air Force F-15E, F-16 and F-22 and the Coast Guard HH-65 helicopter.
So far this year, NORAD has scrambled or diverted aircraft to respond to airspace violations 43 times nationwide, Humphreys said. Suspect planes were intercepted in 19 of those cases. At that pace, the year's totals would be about 77 responses and 32 intercepts, well below the averages since 9/11.
Not every violation involves a plane intruding into closed airspace, Spence said. Some are technical violations, such as using the wrong radio frequency.
NORAD has its headquarters at Peterson Air Force Base, Colo.