NTSB Factual Report

On November 16, 2006, at 1422 Pacific standard time, a Cessna 172, N9522S, encountered wake vortices from an experimental Boeing 747-400 LCF (Large Cargo Freighter), while on a straight-in final approach to a visual approach for landing at Boeing-King County International Airport, Seattle, Washington. The certified flight instructor and her student were not injured, and the aircraft, which is owned and operated by Galvin Flying Service, did not sustain any damage.

According to the flight instructor, who's student was established at 1,000 feet mean sea level (msl) on a straight-in approach to Runway 13 left, about five seconds after being passed by the 747, which had been cleared for a visual approach to runway 13 right, the Cessna 172 rolled almost instantly to a 90 degree right bank, and descended in a nearly straight nose-down attitude. The flight instructor took control of the aircraft, and was able to complete a recovery approximately 150 feet above the channel of water that runs along the east side of Terminal Island. The recovery was completed below the level of the booms of the cranes that were unloading the nearby container ships.

According to Boeing Aircraft Company, the 747 LCF, which at the time of the event was configured for overweight landing tests, weighed approximately 633,700 pounds at the time it passed the Cessna 172 on final approach.

At the time of the incident there was a nine knot crosswind blowing approximately 80 degrees from the right of the path of both aircraft.

A review of the recorded radio transmissions revealed that the Cessna first contacted the tower controller at 1419:22, which was approximately three and one-half minutes prior to the upset. At that time, the flight instructor advised the tower that they were inbound over Ballard Locks, which is approximately seven nautical miles north of the end of the runway, and about a mile and one-half to two miles east of the extended centerline of runway 13 left. The instructor also advised the tower that they had ATIS information X-ray. The controller then advised the Cessna that they had traffic "behind and to your right," and that the traffic was a "seven forty seven heavy jet approaching Shilshole on the localizer," and then cleared them to make a "straight in approach" to runway 13 left. The instructor responded with "Traffic in sight." At 1419:56, the 747 contacted the tower and reported "Ten miles, for landing on the visual." The controller advised the 747 to follow a T-33 that was south of Elliott Bay, and cleared its crew to land on runway 13 right. About fifteen seconds after it checked in, the 747 was advised that in addition to a banner towing aircraft over downtown Seattle, the Cessna was north of Elliott Bay at 1,400 feet, inbound from Ballard. The 747 crew advised the tower that they had the banner tower in sight, but that they were still looking for the Cessna. About 20 seconds after advising the 747 of the banner-tow and Cessna traffic, the tower advised the Cessna that the "heavy 747" was two miles off to their right, that it was "outside the shoreline," that it was landing on the right runway, and that it "does not have you in sight." The flight instructor responded to that transmission by advising the tower that they had the heavy traffic in sight, and then requested that the tower let the 747 know that they (the 172) were about one mile to the northwest of the Space Needle. The tower passed that information on to the 747, and the 747 crew advised the tower that they were still looking for the 172. Then about 10 seconds later, the tower asked the 172 to verify that they had sight of the "heavy jet" off to their right. The instructor pilot responded that they did have "the heavy jet off our right in sight," and then requested a "low approach on runway 13 left." The tower then cleared the 172 for a low approach, and advised the pilot to "...maintain visual separation with the 747 off to your right." The controller also advised the 172 that the 747 did not have them in sight, and then stated "caution wake turbulence." The instructor pilot continued to keep the descending 747 in sight, and the 747 eventually passed the 172 while at an altitude slightly above it. This temporarily created the situation where the 172 was slightly lower than the 747, behind the 747, and downwind of the 747's ground track. At 14:22:45, with the 747 approximately one-quarter mile in front and to the right of the 172, the 172 encountered the vortices generated by the heavy 747.

NTSB Probable Cause

The instructor pilot's improper in-flight decision not to take evasive action as a heavy aircraft passed by while on an upwind parallel approach path to an adjacent runway, leading to a wake vortices encounter. Factors include a nearly direct crosswind blowing from the heavy aircraft toward the incident aircraft.