Colombia

Controlled flight into terrain (CFIT) after the airplane entered adverse weather conditions while cruising under visual flight rules.
The following contributing factors were identified:
- Deficiencies in the effective control and monitoring of flights by the operations; adequate control or monitoring of the flight by the operator was not evident.
- Deficiencies in dispatch procedures; insufficient provision of preflight meteorological information.
- Deficiencies in the inspection, monitoring, and oversight procedures by the Aeronautical Authority.

The accident was the consequence of the combination of the following factors:
- A loss of control in flight as a result of a decrease in minimum control speed and drag, caused by a loss of power on the left engine (n°1);
- A failure of the propeller feathering system on engine n°1, caused by an excessive amount of grease accumulated in the blade coupling section, which prevented the propeller from being feathered quickly (or feathering at all) when the crew attempted to do so. The uncontrolled rotation of the propeller (spinning) created significant drag and made it more difficult to control the aircraft.
- The confirmed loss of power on the left engine, of undetermined origin, was probably caused by a turbocharger malfunction;
- An excess aircraft weight (approximately 770 lb or 349 kg above the MTOW), contributed to the aircraft's inability to accelerate and climb.
The following contributing factors were identified:
- Deficient operator processes in the preventive maintenance of the propellers, failing to detect and allowing the accumulation of grease in the blade coupling section, a circumstance that delayed or prevented the propeller from feathering in a critical phase of flight.
- Failure by the operator to comply with the requirements established by Supplement Type STC SA00192SE in order to operate aircraft HK-5121 with an increased MTOW of 7,352 lb, consisting of:
• Incorporating an FMS (flight manual supplement) into the operation to ensure that no more than four vortex-generating flaps (or blades) were missing.
• Not extending the length of the aircraft's wings or installing winglets.
- Failure by the Operator to comply with the procedures for preparing the Weight and Balance form, by not recording the exact weight of each of the occupants and, instead, using average weights that led to a Takeoff Weight (TOW) lower than the actual weight.
- The operator's lack of knowledge of the impact on the aircraft's MTOW, the altitude of the aerodrome, and the ambient temperature, which at Olaya Herrera aerodrome is lower than the operating MTOW of 7,000 lb corresponding to operation in standard atmosphere.
- The operator did not have a risk analysis for each of the company's operating aerodromes, establishing weight limits for takeoff, taking into account the aircraft's performance charts, the specific operating conditions, and the possible failure of an engine during takeoff or initial climb.