An instructor pilot described an evasive maneuver during a near miss with an air carrier aircraft near Class B airspace.

Narrative

My student and I were on a local training flight and returning to the airport from the practice area that we normally use. We had descended in order to be under the 1800 FT shelf of the Bravo airspace; and were continuing a cruise descent to traffic pattern altitude. We were headed south in order to set up for the 45 degree entry in to the right hand traffic pattern at our home airport. As we neared the airport; my student noticed an airliner slightly above us and headed directly towards us. He pointed out the airplane to me and asked if we should attempt to evade it. Since we were very close and on what appeared to be a collision course; I took control and banked away from the Saab airliner to my right. As we banked away; I watched them bank away to their right. I estimate that we were 200 to 300 FT below them. In order to avoid this type of situation in the future; I will work harder to see and avoid traffic in all phases of flight. I will also encourage my students to spend as much time as possible scanning for traffic.