What happened
On September 28, 2021, a Bell 206L3 helicopter, registration HK4311, was performing a VFR mission to inspect electrical interconnection lines. During the flight, at approximately 13:21 local time, the pilot observed fluctuating oil pressure indications in the engine. Despite these abnormal readings, the pilot elected to continue the flight toward Matecaña Aerodrome (SKPE).
During the final approach to runway 08, while at an altitude of approximately 50 feet AGL, the engine experienced a significant drop in N2 indications and an increase in Turbine Outlet Temperature (TOT), followed by a complete engine shutdown. The loss of power caused the aircraft to lose altitude and result in a heavy landing on the runway surface. All four occupants—comprising the pilot, a technician, and two operators—evacuated the aircraft safely without injuries.
The investigation
The GRIAA investigation focused on the mechanical failure of the powerplant and the decision-making process of the crew. Investigators examined the engine components and found that a malfunction in bearing No. 8 had released metal debris into the lubrication system. This debris caused the oil pump shaft to jam and eventually break, severely restricting internal lubrication.
Evidence from a portable GPS and cockpit video recordings confirmed that the oil pressure had been fluctuating between 10 and 150 PSI for over an hour prior to the landing. The investigation also reviewed maintenance records, noting that a report of turbine noise and instrument oscillations had been recorded just five days before the accident, which likely indicated the onset of the bearing failure.
Findings
- The primary cause of the heavy landing was the uncommanded engine shutdown during final approach.
- The pilot's decision to continue the flight despite evident abnormal engine indications led to operating the engine under extreme conditions with limited lubrication.
- The crew failed to follow the Helicopter Flight Manual (RFM) emergency procedures regarding fluctuating oil pressure, which required an immediate forced landing.
- A mechanical failure in bearing No. 8 released debris that caused the breakage of the oil pump shaft.
- An excess of confidence influenced the pilot's decision-making, preventing the execution of necessary emergency maneuvers.