While on a VFR straight-in approach in a Cessna 172, the flight instructor and her student were advised by the tower that a heavy Boeing 747, which was behind and above the 172, was executing a visual approach to an upwind parallel runway. Although the 747 crew did not have the 172 in sight, the flight instructor in the 172 spotted the 747 soon after being advised of its presence by the tower. The instructor maintained visual contact with the descending 747, and as the 747 neared a point where it would pass the 172, the instructor elected to continue the VFR approach at about the same altitude and on the same course as before. The instructor then watched as the still-descending 747 passed upwind of the 172 at a slightly higher altitude than the 172 was at. When the 747 reached a point about one-quarter mile in front of the 172, the 172 encountered the wake vortices from the 747, and immediately departed controlled flight. Recovery was completed about 150 feet above the terrain. At the time that the 747 passed the 172, the instructor was aware that there was a nine knot wind blowing almost directly across the parallel flight paths of the two aircraft, and although the instructor had requested a low approach at the runway, the instructor did not take evasive action when the 747 passed the 172 while on approach.

The National Transportation Safety Board determines the probable cause(s) of this incident as follows:

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