Colombia

The accident was the consequence of a controlled flight into terrain after the decision of the pilot to continue the flight under VFR mode in IMC conditions.
The following contributing factors were identified:
- The pilot took the decision to continue the flight to destination instead of returning to Flandes (Girardot) or to divert to the alternate airport,
- A low situational awareness on part of the pilot who failed to take into account the geographical environment and to maintain a safe separation from the terrain.

The investigation determined that the accident was caused by the following probable causes:
- Emergency landing of the aircraft on an unprepared field, as a result of a decrease in power, generated by engine failure.
- An engine failure caused by the fracture of three (3) blades of the rotor disk of the high pressure compressor, which caused severe backwards damage to the hot and power section.
Contributing Factors:
- Non-compliance in the engine maintenance process, of what was ordered in AD. No. 2014-17-08R1 FAA (year 2014), which establishes the replacement of the engine blades high pressure compressor in anticipation of material failures in these components.
- Deficient maintenance processes by the provider of this service to the aircraft HK4669G, by not detecting the condition of the high-pressure rotor blades in the boroscopic inspections of the high pressure during routine boroscopic inspections.
- Deficient verification of the Operator's contracted maintenance processes, by not verifying the quality and compliance the quality and full compliance of these processes by the maintenance service provider.

The investigation determined that the accident was caused by the following probable cause(s):
- Loss of in-flight control as a result of slowing below Minimum Control Speed and drag, generated by the failure of the right engine (No. 2).
- Failure of engine No. 2, due to lack of lubrication, possibly caused by oil leakage through an 11.5 mm fracture, found in one of the sides of cylinder No. 2 at the height of the intake valves.
- Inappropriate application by the crew of the emergency procedure for landing with an inoperative engine, by not declaring the emergency, not feathering the propeller of the inoperative engine and configuring the aircraft early for landing (with landing gear and flaps) without having a safe runway, making it difficult to control the aircraft and placing it in a condition of loss of lift and control.

Contributing Factors:
- Failure of the operator to emphasize in the crew training program the techniques and procedures to be followed in the event of engine failure, among others, the declaration of emergency to ATC, the flagging of the propeller of the inoperative engine, the care in the application of power to the good engine so as not to increase yaw and not to configure the aircraft until landing has been assured.
- Lack of emergency calls by the crew, which denotes deficiencies in the Operator's Safety Management System, and which prevented the early warning of the aerodrome support services and deprived the crew of possible assistance from other aircraft or from the same operator.

A loss of in-flight control of the aircraft due to possible excess weight. The aircraft probably managed to take off due to "ground effect", but, once in the air and out of ground effect, it was not able to obtain the speed that would allow it to safely accomplish the climb.
Contributing Factors:
- Absence of Dispatch procedures of the operator to perform a correct Weight and Balance of the aircraft, and the effective control of the boarded cargo.
- Incorrect calculation of the weight and balance of the aircraft by the crew, by not considering all the cargo that was loaded, causing the aircraft to take off with a possible excess weight.
- Weak operational safety management processes of the operator by not considering the operating characteristics of airfields such as Popayán (high altitude, high ambient temperature) that significantly limit the operation.

The investigation determined that the accident was caused by the following probable causes:
- Loss of control in-flight as a consequence of the decrease in minimum in-flight control speed and drag generated by the impossibility of performing the No. 1 engine propeller feathering in the face of engine failure.
- Malfunction of the lubrication system of engine No. 1, evident in the abundant oil leakage from the engine, in flight, and in the governor of the left propeller; although discrepancies were found in the maintenance of the propeller feathering pressure line, it was not possible to determine the origin of the oil leakage.
- Weaknesses in the aircraft Operator's operational procedures, lacking a standard that would facilitate a crew's decision making to act in the event of critical failures, in matters such as making an emergency landing on unprepared field or the selection of an alternate airfield.

Contributing Factors:
- Deficiencies in standard maintenance practices during repairs performed on the No. 1 engine's propeller propeller feathering oil pressure line.
- Non-compliance with an effective and reliable maintenance program, which did not verify the operating conditions of the aircraft components; it was not possible to determine compliance with the last 50-hour service, Phase A, to engine No. 1 according to the company's maintenance program, since there are no records of that service in the Flight Log.
- Inefficient safety management system of the Operator for not detecting errors in the maintenance processes and in the conduct and control of operations.