What happened
On 3 April 2024, a Bell TH-1H helicopter, tail number 74-22313, was conducting a flight evaluation at Skelly Stagefield Army Heliport, Alabama. The aircraft, assigned to the 23d Flying Training Squadron (23 FTS) under the 58th Special Operations Wing, was performing a transition checkride for three student pilots accompanied by an instructor pilot.
During slope operations, the student pilot initiated a takeoff that caused the left skid to lift from the ground. The pilot misidentified the aircraft's orientation, believing it was level when it was actually in a 2-to-5 degree right bank. Perceiving a leftward slide, the student pilot applied right cyclic input, increasing the right bank to between 6 and 10 degrees. While the instructor pilot attempted to counter this with left cyclic input, the maneuver was ineffective due to the opposing inputs from the student. Believing the aircraft had stabilized, the student pilot increased power to lift off. This increase in collective, combined with the existing bank angle, triggered a dynamic rollover where the main rotor blades struck the ground, leaving the aircraft on its right side.
The investigation
The Air Force Accident Investigation Board examined the sequence of flight inputs and the physical state of the aircraft. Investigators reviewed maintenance records, weather conditions, and aircrew training progress. The board evaluated the mechanical integrity of the Bell TH-1H, specifically examining the mast, rotor head assembly, and transmission following the impact. The investigation also reviewed the crew's physiological and medical readiness, as well as the technical orders governing slope operations.
Findings
- The primary cause of the mishap was spatial disorientation of the student pilot, which led to erroneous control inputs.
- The student pilot misperceived a rightward bank as a level attitude and subsequently applied incorrect cyclic corrections.
- The instructor pilot provided insufficient corrective action by failing to reduce the collective power, which is the recommended procedure for controlling rolling motions during such events.
- The combination of an increased bank angle and increased collective power caused the aircraft to exceed its critical rollover angle.
- No mechanical failures, environmental factors, or medical issues were identified as contributing to the event.