What happened
On August 22, 2017, a private flight departed from Sandefjord Airport Torp in an Aviat Aircraft Inc. Pitts S-2B, registration LN-PTS. The flight, consisting of the pilot and one passenger, initially proceeded toward the Holmest and Sandefjord areas. While operating within the Torp control zone, the aircraft exceeded its cleared altitude of 1,500 ft, reaching heights of approximately 2,500 ft.
Radar data and witness accounts indicate that the aircraft performed several maneuvers, including a loop that reached an altitude of 3,000 ft. Shortly before the accident, the aircraft entered a rapid vertical climb from 1,900 ft, reaching a peak of approximately 2,900 ft. At the apex of this climb, the aircraft's airspeed decreased until it momentarily became stationary in the air. The aircraft then fell backward, entering a left-hand inverted spin. The pilot was unable to recover control, and the aircraft struck the ground near Ekeberg school, resulting in two fatalities.
The investigation
The Norwegian Safety Investigation Authority (NSIA) examined radar data, witness testimonies, and video recordings of the event. The investigation focused on the pilot's proficiency, the aircraft's weight and balance, and the regulatory framework regarding aerobatic flight. Investigators noted that the pilot had recently performed a self-familiarization on the LN-PTS and possessed limited experience with this specific model. Furthermore, the investigation found that the aircraft's empty weight and center of gravity were not properly utilized for mass and balance calculations during the flight preparation.
Findings
- The pilot lacked the necessary training and specific rating required to perform aerobatic maneuvers.
- The pilot lacked the sufficient skills to manage a stall turn or hammerhead maneuver, which subsequently led to the uncontrolled inverted spin.
- The aircraft's mass and balance calculations were inaccurate because the current empty weight and center of gravity were not properly assessed.
- The pilot's recent familiarity with the aircraft model provided insufficient understanding of its specific handling characteristics.
Safety action
The NSIA issued a safety recommendation to the Civil Aviation Authority Norway, urging the implementation of better "Safety promotion" regarding the importance of adhering to aircraft manual limitations. The authority should also implement measures for more rigorous probability assessments when performing aircraft weighings to ensure accurate center of gravity data.