What happened
During a night-time medical transport mission conducted under instrument flight rules, an aircraft was traveling to a neighboring island to retrieve a patient. Approximately 13 minutes into the flight, while at an altitude of 13,000 feet mean sea level, the aircraft experienced a failure of its vertical gyro. This malfunction led to the failure of the pilot's Electric Attitude Director Indicator (EADI) and the subsequent disconnection of the autopilot.
Following these failures, the pilot transitioned to manual flight, relying on the co-pilot's attitude gyro for pitch and bank information. The pilot did not notify air traffic control of the instrumentation failure or the autopilot's disengagement. During the flight, the aircraft underwent several oscillations, including right banks and a left turn. Although the pilot agreed to a course change requested by air traffic control, the aircraft entered a steep, descending right bank.
As the flight progressed, the aircraft's descent rate increased from 1,000 feet per minute to 3,500 feet per minute as airspeed rose. During a period of communication with air traffic control, the aircraft reached a 65-degree bank angle. As the pilot attempted to verify his heading, the bank angle increased to 90 degrees and the airspeed surpassed 260 knots. A loud metallic sound, consistent with the separation of the empennage from the fuselage, was recorded before the aircraft struck the water. The wreckage was later found on the ocean floor at a depth of approximately 6,420 feet.
Findings
- The failure of the vertical gyro caused the loss of the pilot's primary attitude information and the autopilot.
- The pilot failed to declare an emergency or report the loss of instrument functionality to air traffic control.
- The aircraft entered an increasingly steep and rapid descent, leading to high speeds and structural failure.