What happened
On January 31, 2024, at 14:40 local time, an AS-3HD B3 helicopter, operated by the Chilean Investigative Police (PDI) for a police aerial mission, departed from the Pichidangui Aerodrome in the Coquimbo Region. The flight crew, consisting of a pilot in command and a second pilot, was accompanied by three passengers.
Immediately following a vertical takeoff, the aircraft transitioned into out-of-ground-effect flight and turned toward a heading of 270°. During this maneuver, the crew heard unusual noises, prompting an attempt to land the aircraft. The helicopter experienced a sudden yaw to the right and a rapid descent, striking a perimeter fence made of wooden posts. The impact caused a post-crash fire that consumed the aircraft. While all occupants managed to evacuate the wreckage, the pilot in command and one passenger tragically died from their injuries at medical facilities. The second pilot and the remaining two passengers sustained various injuries.
The investigation
DGAC Chile examined the maintenance history and the mechanical state of the aircraft following the accident. The investigation focused on a recent "Great Visit" (144-month heavy maintenance inspection) performed by a maintenance center. Investigators analyzed the engine-to-main gearbox coupling shaft and the installation of the engine shaft flange bolts.
Technical inspections revealed that during the recent heavy maintenance, the MGB/Engine Coupling Shaft had been disassembled and reinstalled. The investigation also reviewed the operational environment of the maintenance facility, noting that technicians were working under pressure, extended shifts, and frequent interruptions. Furthermore, the presence of two 35-liter fuel canisters inside the cabin was evaluated regarding their role in the fire's spread.
Findings
- The primary cause of the accident was the disconnection of the MGB/Engine Coupling Shaft during takeoff, which severed the power flow from the engine to the main rotor.
- This disconnection was caused by an incorrect assembly of the shaft, likely due to the improper installation of bolts 1, 3, and 5 of the Engine Shaft Flange.
- The maintenance environment contributed to the error, as high operational pressure and long working hours increased the risk of human error during complex technical tasks.
- The post-crash fire was intensified by the rupture of the standard fuel tank (which lacked a Crash Resistant Fuel System) and the presence of additional fuel canisters inside the cabin.
Safety action
- The maintenance center must reinforce internal control and verification procedures for the assembly of critical components and implement cross-inspections for high-risk tasks.
- Maintenance providers should manage fatigue by controlling overtime and ensuring adequate rest periods for technicians.
- The operator should update its Operations Manual to prohibit the transport of fuel canisters inside the cabin, suggesting instead the use of external containers or approved transport methods.
- It is recommended that the operator study the feasibility of installing Crash Resistant Fuel Systems (CRFS) in their fleet.