Washington National airport, the close-in airport for DC, has strict rules for routing landings and departures. This is both the result of noise restrictions but also for security. Planes come close to national monuments and even the White House. Deviate and fighter jets can scramble. Miss and approach and you can get sent to Dulles airport.
Most of downtown D.C. below 18,000 feet is prohibited airspace. There’s a narrow path pilots have to fly, that’s pretty cool for passengers. The River Visual approach causes aircraft to hug the Potomac and turn just before landing.
Flights taking off to the North climb quickly and turn left — one doesn’t want to get shot down approaching the Washington Monument and White House!
The Toronto flight:
departed Ronald Reagan National Airport’s runway 01, takeoff clearance included a traffic advisory of a helicopter at 200 feet in the departure path, and was handed off to Potomac Departure, but did not report on Potomac Depature frequency. The aircraft crossed through a no-fly zone near the Capitol prompting authorities to raise their security level. Radio contact with the aircraft was subseqently re-established. The aircraft continued to Toronto for a safe landing on schedule.
After radio contact was restored the alert was cancelled.
Pilots are trained in this area before being allowed to fly through it. The Air Wisconsin pilots were certainly aware of the restrictions, and the need not to deviate course or lose communication. The helicopter in the departure path may be a clue, with pilots more concerned with air traffic in their vicinity than switching communication frequency quickly enough and making their required turn.
This wasn’t much of a deviation, but it doesn’t take much.
Raising the security level almost certainly meant starting the process towards preparation for intercept. Thank goodness communications were re-established quickly.