Narrative:

After takeoff; climbing out on the ARSNL4 departure and turning to intercept the course to gadzi intersection; we were at 1;100 feet when I heard and saw the warning of another aircraft. The advisory system showed 00 foot difference in altitude and the yellow warning dot was superimposed on top of our aircraft.I looked out and saw another single engine aircraft heading directly for us at coequal altitude. At that point I yelled to the pilot and took control of the aircraft and dove left to avoid a collision. The pilot of the other aircraft made a turn to the right to reenter the traffic pattern. We continued with our flight.after returning to hef; we contacted potomac approach and the manassas tower manager. The hef's manager said his tower controller had lost sight of the plane on radar and thought he had turned into the pattern. When the other plane reappeared on the radar it set off a collision alarm. Potomac's alarm went off about the same time as we called in to report the near midair collision.in asking questions of the tower manager; we found out the other pilot was a student pilot who was supposed to be in the closed traffic pattern; but had climbed straight out toward pattern altitude before turning.seems to be a controller not paying attention and launching a plane on parallel runway within seconds of clearing us for takeoff. Second; had the controller known it was a student pilot; she would have watched him closer. Recommend solo student pilots announce that to the controllers so they can watch them and be aware of those planes.

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Original NASA ASRS Text

Title: An instructor pilot took the aircraft from his student at 1;100 feet to take evasive action during a near miss with a student pilot who strayed from the HEF closed pattern.

Narrative: After takeoff; climbing out on the ARSNL4 Departure and turning to intercept the course to GADZI intersection; we were at 1;100 feet when I heard and saw the warning of another aircraft. The advisory system showed 00 foot difference in altitude and the yellow warning dot was superimposed on top of our aircraft.I looked out and saw another single engine aircraft heading directly for us at coequal altitude. At that point I yelled to the pilot and took control of the aircraft and dove left to avoid a collision. The pilot of the other aircraft made a turn to the right to reenter the traffic pattern. We continued with our flight.After returning to HEF; we contacted Potomac Approach and the Manassas Tower manager. The HEF's Manager said his Tower Controller had lost sight of the plane on radar and thought he had turned into the pattern. When the other plane reappeared on the radar it set off a collision alarm. Potomac's alarm went off about the same time as we called in to report the near midair collision.In asking questions of the Tower Manager; we found out the other pilot was a student pilot who was supposed to be in the closed traffic pattern; but had climbed straight out toward pattern altitude before turning.Seems to be a controller not paying attention and launching a plane on parallel runway within seconds of clearing us for takeoff. Second; had the controller known it was a student pilot; she would have watched him closer. Recommend solo student pilots announce that to the controllers so they can watch them and be aware of those planes.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.