Colombia

Probable causes:
- Controlled flight into terrain during the execution of the IFR departure procedure VVC2A, during which the crew mistakenly turned left, contrary to the procedure, heading towards the mountainous area at the foothills of the eastern range, where the impact occurred.
- Loss of situational awareness by the crew, which, for reasons that could not be determined, apparently made a controlled left turn, contrary to the indications of the VVC2A departure procedure, even though it was an experienced crew familiar with the operating area.

The following contributing factors were identified:
- Lack of operator standards, as there was no detailed, organized, and sequential instructional plan and syllabus for the crew to follow during each maneuver, such as the VVC2A instrument departure.
- Lack of operator standards, as there was no specific syllabus for the planning and execution of the Recurrent Check, taking into account, among other aspects, the composition of the aircraft crew, consisting of two instructor pilots, one of whom was conducting the check on the other.
- Inadequate planning and supervision of the training flight by the operator, as they did not conduct a specific risk analysis of the flight, did not monitor its preparation and execution, did not provide details in a flight order or other document, considering especially the composition of the aircraft crew, consisting of two instructor pilots, one of whom was conducting the check on the other.
- Deficient planning and preparation of the flight by the crew, as they informally changed the VFR Flight Plan to IFR, apparently did not conduct a complete and adequate briefing, were unaware of or did not consider the VVC2A SID for the start of the IFR flight, and omitted several IFR flight procedures.
- Crew's neglect of the following IFR flight procedures:
- Not specifying a route and an IFR departure procedure in the IFR Flight Plan.
- Not requesting complete authorization from ATC to initiate an IFR flight. At no time did they mention the VVC2A departure, which was key to the verbally proposed plan before takeoff.
- Not defining or requesting from ATS which standard departure procedure or other they would use to initiate the IFR flight, in which they would encounter IMC shortly after takeoff.
- Not requiring ATC to assign a transponder code before takeoff or at any other phase of the flight, or selecting code 2000 as they did not receive instructions from ATS to activate the transponder.
- Likely not activating the transponder before takeoff and/or not verifying its correct operation before takeoff or immediately once the aircraft was in the air.
- Inaccurate use of phraseology with non-standard terminology in their transmissions with ATC.
- Insufficient experience and training in IFR flights by the crew, despite their extensive experience with the equipment. Much of this experience had been gained in the eastern region of the country, where the majority of DC3 flights are conducted in VMC and under VFR, with no opportunity for the practical execution of IFR procedures.
- Overconfidence of the crew, influenced by factors such as the high flight experience and DC3 equipment experience of the two pilots in the crew, their status as instructor pilots, the relatively low operational demand of the flight mission, and the knowledge, familiarity, and confidence of both crew members with the aerodrome's characteristics, the surrounding area, and especially the peculiarities and risks of the terrain to the west of the takeoff path.
- Non-observance by air traffic control of the following IFR flight procedures initiated by HK2820:
- Failure to issue complete authorization to the aircraft for the IFR flight before initiating the flight or at any other time.
- Failure to issue a standardized instrument departure, SID, or any other safe departure procedure to the aircraft. At no time did ATC mention the VVC2A departure, which was crucial for carrying out the plan verbally proposed by the crew.
- Failure to provide the aircraft with a transponder code before takeoff or at another appropriate time, or to verify its response. This process started only 03:11 minutes after the aircraft took off, so positive radar contact verification was only achieved 04:58 minutes after takeoff, delaying radar presentation and limiting positive flight control.
- Late transfer of aircraft control from the Control Tower to Approach Control (03:35 minutes after takeoff), not immediately after the aircraft was airborne as it should have been, considering prevailing IMC flight conditions in the vicinity of the aerodrome.
- Operating with an incomplete radar display configuration in Approach Control, with insufficient symbology, depriving control of references and judgment elements for an accurate location of the aircraft and its left turn from the path.
- Failure to observe radar surveillance techniques and procedures.
- Inaccurate use of phraseology with non-standard terminology in their transmissions with the aircraft.
- Lack of situational awareness by both the crew and ATC during a flight that, perhaps because it seemed routine, led both parties to omit elementary IFR flight procedures, disregarding the inherent risks of an operation in IMC conditions, with strict IFR procedures that needed to be followed, considering, among other things, the aerodrome's proximity to a mountainous area.

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.

The accident was the consequence of a lateral runway excursion as a result of a loss of control on the ground caused by the loss of air pressure in the left main gear tire, as a result of the penetration of a FOD (metallic object) into the tire during the landing run. Poor risk management by the San Felipe Aerodrome operator (SKFP) and a lack of a runway FOD control program (SKFP) by the operator of the aerodrome was considered as contributing factors.

A loss of control during the takeoff roll as a result of inappropriate techniques on the part of the pilot-in-command who suffered a loss of situational awareness by not detecting the deviation in a timely manner.
The following contributing factors were identified:
- Inadequate crew decisions to apply appropriate corrective actions,
- Inadequate crew training program,
- Poor operational supervision on part of the operator.

The following findings were identified:
- Inappropriate decision by the aircraft operator to rush the aircraft's initial route to an aerodrome unknown to the company, not appropriate to the type of aircraft and not authorised in its Operating Specifications, without at least a proper risk assessment.
- Inadequate crew decision to accept and decide to proceed to an unknown aerodrome, without due knowledge of its characteristics, without prior experience or training in aerodrome operation and without at least a risk assessment.
- A side runway excursion, from 24 metres from the threshold of runway 25, as a result of a probable unstabilised approach resulting in an off-axis landing.
Contributing factors:
- Inefficient planning and supervision of operations by the aircraft operator, by scheduling the operation to an unknown airfield.
- Failure of the company to comply with the contents of the Dispatch Manual and General Operations Manual, in relation to the procedures that must be complied with before operating new routes, new airports or special airports, in aspects such as route analysis, runway analysis, risk management and crew requirements.
- Ignorance of the Tarapacá runway by the crew.