20090704021669A

On July 4, 2009, at approximately 1330 PDT, an aero vodochody L-29, N97869, impacted the ground on old town road in Tehachapi, California. Both occupants of the aircraft were pronounced dead at the scene by the kern county corner's office. The accident site is approximately three nautical miles southwest of Tehachapi airport (tsp). The mishap aircraft was part of a three ship formation performing a flyby over central park for the 4th of July celebration located within 2 densely populated/congested area in Tehachapi, California. All three aircraft performing in the celebration were aero vodochody L-29S and are certificated as experimental exhibition. Additionally, these aircraft had performed two flybys of the 4th of July parade over Tehachapi on the morning of the 4th at approximately 1030. Two of the three aircraft performing for the 4th of July celebration were members of the thunderdelphins demonstration team. The mishap aircraft was not a member of the demonstration team. The third member of the demonstration team was unable to make these flights due to a mechanical problem. The owner of the mishap aircraft was in the front seat of the aircraft during the mishap. He was not a formation qualified pilot, nor was he an aerobatic qualified pilot. Additionally, he did not have any military flight experience. The pilot in the back seat of the mishap aircraft was a former military pilot and a flight test pilot for northrop Grumman. He was an FAA certified training center evaluator (tce) on the A-320 and worked for flight training international an FAA certificated part 142 school. He was formation qualified in the L-29 and L-39. Additionally, he was a retired united air lines captain. The city of Tehachapi, has, for the past several years, employed the services of the thunderdelphins, an L-29 demonstration team, to perform flybys at their 4th of July celebration. The planned route of flight, on the first flight, was to takeoff single ship on runway 29 at tsp, make a left turn to head east, south of the city, and rejoin as a three ship formation. Once southeast of the city, they planned to execute a left turn heading west to fly over the parade at 2000 feet a right tear drop turn back to the east for a second pass over the parade from east to west at 1000 feet AGL. The flight then would execute a slight right turn to a tear drop left turn to setup for the overhead approach, with a left break, at 1000 AGL for a landing at tsp on runway 29. The plan for the afternoon sortie was to be the same except for the flyby over central park, single ship in trail at approximately 2000 foot spacing, east to west, for the flag raising ceremony. The flight then would rejoin after the first flyby of the park during the tear drop right turn to execute a second flyby of the park. The flight of three planned to turn slightly to the right and then execute a left turn to setup for the overhead approach with a left break at 1000 feet AGL. Several eyewitnesses were interviewed concerning these flybys. These witnesses stated that these flybys were very low over the parade route and the park. These witnesses estimated that these aircraft executed the flybys at 300 to 400 feet AGL. One witness, the brother of one of the pilots in the mishap aircraft, supplied a video of the flybys over the parade route from the morning sortie. Another witness supplied video of the afternoon flyby over the park just minutes before the mishap. Both these videos show these aircraft executed the flybys well below 1000 feet AGL. The pilots of the flight of three did have a briefing prior to both flights. However, these briefings only covered the takeoff procedures and procedures in the event that if one of the aircraft encountered a problem in flight for an emergency return. These briefings did not include route of flight, altitudes along the route flight, rejoin procedures, or route study for terrain and obstacles. On July 4, 2009, at approximately 1315, the flight of three departed tsp single ship on runway 29. The lead aircraft had a passenger onboard for this sortie, the mayor of Tehachapi. The number two aircraft had a passenger on board the aircraft, an employee of the city of Tehachapi department of airports. His passenger is a student pilot and flies out of the Tehachapi airport. The mishap aircraft was in the number three position. The flight of three executed a left turn after departure and headed east, just south of the city of Tehachapi. The flight then turned left to head west for the flyby over the park. The flight of three executed the flyby over the park well below 1000 feet AGL. One witness in the park, who is an employee of the Tehachapi police department, stated that she heard the aircraft approaching, turned to look, and instinctively ducked because they were so low. Additionally, on the video of the flyby over the park, as the number three aircraft, the mishap aircraft, passes over the park, the witness states, "look at this guy he is really low." The flight of three, in single ship formation in trail, after the flyby of the park, executes a slight left turn heading southwest along the mountains south of highline blvd. The number two aircraft rejoins in loose fingertip formation on leads left wing. The number three aircraft is still in trail and slightly below lead and number two. All three aircraft according to several eyewitnesses including the passengers stated they were at or just below the ridgeline. The ridgeline in this area is approximately 4400 to 4700 feet mean sea level (MSL). The area near the accident site is approximately 4000 feet MSL. The flight executes a right turn with the lead and number two aircraft in formation. According to several eyewitnesses the number three aircraft was catching up to the formation very quickly. As the formation turned right, the number three aircraft execute a cutoff maneuver while the formation was in a right turn at approximately 400 feet AGL. As the number three aircraft. According to several eyewitnesses, the number three aircraft pitched up and rolled left over the formation and ended up heading down below the formation. The eyewitnesses on the ground, along old town road, stated the aircraft headed straight down, turned to the left, heading north, and the ground in a field and skidded onto old town road. The aircraft came to rest on old town road. The post crash fire charred the remains of the aircraft, and the aircraft was destroyed. The maneuver that eyewitnesses describe is commonly known as a "lag roll." The lag roll maneuver was employed by fighter pilots in world war ii, korea, and vietnam. This maneuver was used to deplete excess energy during combat to prevent you from passing your target. This maneuver requires a high degree of skill and practice to perform correctly. This maneuver is no longer utilized by modern day air forces and has not been taught by the us air force since the early 1970'S. Pilots selected by the us air force as test pilot candidates are taught this maneuver as part of their qualification training. However, according to the us air force test pilot school, edwards air force base, accomplished fighter pilots have trouble mastering this maneuver. Factors affecting the accident lack of comprehensive mission planning and route study contributed to this mishap. Additionally, the lack of continuation training for operations in the low level arena also contributed to this accident. The us air force routinely operates in the low level arena. Additonally, they perform these missions three to five times a week as part of required continualion training. Performing a low level rejoin, on the inside of a turn, caused the mishap aircraft to lose sight of the other aircraft in the formation. Performing this maneuver, at low altitude, in a turn, leaves the mishap aircraft with no options except to execute an extreme maneuver like a "lag roll". Incorrectly performing a "lag roll" will cause the aircraft to lose 500 to 1000 feet of altitude. Incorrectly performinq this maneuver at 400 AGL did not leave the aircraft with enough altitude to recover. Aircraft layout inspection the recovered wreckage of N97869 was examined on July 28, 2009, at the facilities of aircraft recovery services chino, California. The examination of the recovered wreckage revealed the left wing remained attached to the center fuselage section. The right wing was separated from the center fuselage section at the wing root by wreckage recovery personnel. Extensive fire damage was observed around the right wing attach point. The left wing was mostly intact and exhibited fire damage. The outboard four feet of the left wing was separated. The inboard and outboard flap assemblies remained attached to the wing. The inboard portion of the left aileron remained attached to its mounts and the outboard portion of the aileron was separated. He left main landing gear was observed in the retracted position. The left wing auxiliary fuel tank was separated from the wing and was severly crushed. The right wing was intact and exhibited fire damage. The leading edge was crushed aft to the forward wing spar about 5 feet inboard of the wingtip. The inboard and outboard flaps remained attached to the wing. The right aileron remained attached to its mounts. The right main landing gear was observed in the retracted position. The right wing auxiliary fuel lank was separated from the wing and was severely crushed. The forward portion of the fuselage from the nose of the airplane to bulkhead number 10 (aft of the rear seat) was fragmented into multiple pieces and exhibited fire damage. The center section of the fuselage was intact and exhibited severe fire damage. The rear section of the fuselage was separated from the center section of the fuselage near bulkhead number 19 (forward of the wing flap assemblies). The empennage was partiaily separated from the rear fuselage section at the base of the vertical stabilizer. The left speed brake assembly remained attached to the fuselage and was observed in the extended position. The right speed brake, fuselage attach brackets, had impact damage and was separated from the fuselage. The right speed brake hydraulic actuator was observed in the "extended" position. The engine was separated from the fuselage structure. The structure surrounding the fuselage was severely deformed and torn due to impact damage. The horizontal stabilizer remained attached to the vertical stabilizer. The elevator remained attached to the horizontal stabilizer via all mounts. The elevator exhibited fire and impact damage. The rudder and tail cone assembly were separated from the vertical stabilizer. Flight control continuity was established from the elevator and rudder control torque tubes forward to the center fuselage section. The elevator and rudder control torque tubes were fractured in multiple areas. The fractures were consistent with impact related damage and fire damage. Continuity was established from the left and right wing root to the ailerons. Remains of the forward and rear cockpit controls were recovered and exhibited impact related damage. All major components of the cockpit flight control system were located. The recovered components exhibited impact damage. Instruments displaced from the instrument panels were located within the recovered wreckage debris. The airspeed indicator faceplate and indicating needle (position unknown) was displaced irom the instrument housing. The mach/airspeed indicator needle was observed indicating 0.7 mach. The lom M701C-500 RPM indicator gauge was reading about 90% RPM. There were not any indicaticns of pre-impact mechanical anomalies noted with the recovered airframe the engine was seperated into multiple sections. The compressor section was partially intact. Four of the seven combustion chambers were separated from the engine. The compressor centrifugal impeller wheel exhibited severe impact and thermal damage. Rotational scoring and rub marks were observed on the compressor housing and compressor wheel shaft. The turbine section was separated and damaged due to impact. The turbine wheel was intact. All of the turbine wheel blade tips were bent opposite the direction of rotation. The turbine wheel was displaced against the stator assembly. A majority of the stator vanes were separated. Rotational scoring marks were observed around the turbine wheel on the casing. There were not any pre-impact mechanical anomalies noted with the recovered engine components.