Exploring the Possibility of a Low Altitude Gravity Wave Encounter as the Cause of a General Aviation Accident near Norman Oklahoma on December 6, 1998

On December 6, 1998, a general aviation twin engine Beech Baron crashed near Norman Oklahoma. In this paper, we explore the possibility that this accident was due to the meteorological conditions found in the area, specifically low altitude wind shear due to gravity waves (i.e. Buoyancy or density waves). Gravity waves form along a discontinuity boundary of differing densities formed due to thunderstorm outflows within the lower atmosphere. This boundary is perturbed by shearing winds above and below the boundary causing the boundary to undulate in a sinusoidal wave pattern. These waves pose a particular risk to aviation safety since the waves possess characteristics similar to both microbursts and gust fronts. Over the past several years, there have been several incidents in which aircraft have experience airspeed fluctuations as well as severe turbulence when encountering this phenomenon.

Although the Norman accident occurred when there were moderate to severe thunderstorms in the region, none of the storms were within 30nm of the accident site. In fact, the accident occurred in an echo free environment. Although there is no conclusive evidence that substantiates the cause of the accident, we present evidence that suggests that an encounter with the gravity wave phenomenon may have occurred. Radar base data from the KTLX WSR-88D shows the position and movement of the gravity waves in the area of the accident. Flight beacon data was used to establish the location of the aircraft with respect to the position of the gravity waves. In addition, PIREPS and control tower voice transmissions are included to indicate that the pilot as well as other aircraft were experiencing windshear and turbulence around the time of the accident. It appears that the aircraft's flight path and that of the gravity waves coincide in such a way as to the accident may have arisen from an encounter with gravity waves.