Paso Robles Airport
Aircraft Accident/Incident Report

Paso Robles, California 93446
Sunday, December 30, 2007 11:40 PST

As the airplane was approaching a friend's residence, the pilot called the friend on a cellular telephone informing him that he was about to pass by. The pilot had done this on many occasions as a way of notifying the friend that he should leave to pick him up from the airport. The friend was speaking with the pilot on the telephone when he observed the airplane drop rapidly about 1,000 feet as it was flying toward his house. The airplane was maneuvering very low in a nose-high configuration with full power, flying fast through the slight valley about 75 feet above ground level (agl). He noted that the winds were from the east (providing a tailwind) and estimated they were about 40 miles per hour (mph). The friend heard the telephone drop, with the pilot making a few inaudible comments. The airplane than made a rapid ascent as it neared power lines, climbing in a near vertical nose-high maneuver to about 1,000 feet agl. It subsequently made a 90-degree pivot about the longitudinal axis and then continued to turn into a barrel roll, disappearing behind the tree line. Ground scar analysis, impact signatures, and wreckage fragmentation patterns disclosed that the airplane impacted terrain in a near level attitude, with high forward velocity. The impact geometry combined with the witness statements of observing the airplane roll immediately after a near-vertical climb, is consistent with the pilot recovering from an accelerated stall and subsequent roll just prior to impact. There was no evidence of a pre-mishap mechanical malfunction or failure observed during the examination of the engine or airframe. A pilot report in the immediate vicinity and prior to the accident reported continuous light to occasional moderate turbulence between 2,000 and 5,000 feet mean sea level (msl). The GOES-11 satellite imagery surrounding the period depicted orographic clouds over and downwind of the higher terrain and 5 minutes after the accident, showed a band of tubular or "arcus" clouds moving over the accident site, which were similar in appearance to roll clouds. The clouds were of short duration and had moved southeastward and became less distinct about 15 minutes thereafter. Additionally, the Vandenburg AFB soundings surrounding the accident time indicated a strong low-level temperature inversion with northerly winds favorable for mountain wave activity formation downstream from high terrain. Based on an analysis of the terrain, wind flow pattern, and potential arcus clouds over the area, it is likely the accident aircraft encountered moderate or greater turbulence and downdrafts during the flyby of the residence.

The pilot's encounter with isolated moderate (or greater) turbulence, updrafts, and downdrafts associated with localized mountain wave conditions at low altitude, and, his failure to maintain adequate airspeed during the encounter that resulted in an inadvertent accelerated stall. Contributing to the accident were the pilot's decision to conduct low altitude flight maneuver and the pilot's diverted attention while using a cell phone.