NTSB Factual Report

On April 9, 2004, at 1923 eastern daylight time, a Waco ASO, N11253, was substantially damaged during takeoff at Lexington-Bluegrass Airport (LEX), Lexington, Kentucky. The certificated private pilot was not injured. Visual meteorological conditions prevailed, and no flight plan had been filed for local personal flight, conducted under 14 CFR Part 91.

The pilot reported that he had initiated the takeoff roll from a position on the runway where an MD-80 had previously touched down. When the pilot began the takeoff roll, the airplane's tail elevation was normal until it "spontaneously" went higher. The pilot lowered the tail; however, it again went higher, and the propeller hit the runway. The pilot again tried to lower the tail, but it went higher still, with a "heavier contact of the propeller," and the airplane then nosed over. The pilot also noted that, "there seemed to be some lateral turbulence during the takeoff."

According to a Federal Aviation Administration (FAA) inspector, the pilot initiated the takeoff attempt on runway 22, at intersection C. The airplane rolled approximately 200 feet, then nosed over. Two additional FAA inspectors confirmed that the accident airplane entered the runway just after an MD-80 had landed, and when the pilot began his takeoff roll, the MD-80 had just taxied clear of the runway. Runway 22 was 7,003 feet long and 150 wide, and intersection C was about 1,500 feet from the approach end. Winds recorded at the airport, about 15 minutes before the accident, were from 020 degrees true at 3 knots.

According to FAA Advisory Circular 90-23F, "Aircraft Wake Turbulence," wing vortex circulation "is outward, upward and around the wing tips," and "vortices from larger (transport category) aircraft sink at a rate of several hundred feet per minute, slowing their descent and diminishing in strength with time and distance behind the generating aircraft." In addition, "when vortices of larger aircraft sink close to the ground (within 100 to 200 feet) they tend to move over laterally over the ground at a speed of 2 to 3 knots."

The advisory circular also noted that, "a tailwind condition can move the vortices of the preceding aircraft forward into the touchdown zone," and that, "the light quartering tailwind requires maximum caution." It also stated that pilots should be "particularly alert" in conditions where vortices could remain in a touchdown area, and in capital letters stated, "WHETHER OR NOT A WARNING OR INFORMATION HAS BEEN GIVEN, THE PILOT IS EXPECTED TO ADJUST AIRCRAFT OPERATIONS AND FLIGHT PATH AS NECESSARY TO PRECLUDE SERIOUS WAKE ENCOUNTERS."

NTSB Probable Cause

The pilot's inadequate remedial action to wake turbulence. A factor was the pilot's failure to recognize that the takeoff conditions were conducive to wake turbulence.