Plain, Valley

The flight crews encounter with un-forecasted freezing rain resulting in an uncontrolled descent, forced landing, and substantial damage to the airplane's firewall, and forward pressure bulkhead.

The pilot's loss of control due to spatial disorientation while operating in instrument meteorological conditions, which resulted in an exceedance of the airplane's design stress limitations, and a subsequent in-flight breakup. Contributing to the accident was the pilot's reported inflight instrumentation anomaly, the origin of which could not be determined during the investigation.

Findings as to causes and contributing factors:
1. Although the aircraft was prohibited from flying in known or forecast icing conditions, Wasaya Airways Limited Partnership (Wasaya) flight 127 (WSG127) was dispatched into forecast icing conditions.
2. The high take-off weight of WSG127 increased the severity of degraded performance when the flight encountered icing conditions.
3. The pilot of WSG127 continued the flight in icing conditions for about 6 minutes, resulting in progressively degraded performance.
4. WSG127 experienced substantially degraded aircraft performance as a result of ice accumulation, resulting in aerodynamic stall, loss of control, and collision with terrain.
5. The Type C pilot self-dispatch procedures and practices in use at Wasaya at the time of the occurrence did not ensure that operational risk was managed to an acceptable level.
6. Wasaya had not implemented all of the mitigation strategies from its January 2015 risk assessment of Cessna 208B operations in known or forecast icing conditions, and the company remained exposed to some unmitigated hazards that had been identified in the risk assessment.
7. There was a company norm of dispatching Cessna 208B flights into forecast icing conditions, although 4 of Wasaya’s 5 Cessna 208B aircraft were prohibited from operating in these conditions.

Findings as to risk:
1. Without effective risk-management processes, aircraft may continue to be dispatched into forecast or known icing conditions that exceed the operating capabilities of the aircraft, increasing the risk of degraded aircraft performance or loss of control.
2. If pilots operating under self-dispatch do not have adequate tools to complete an operational risk assessment before releasing a flight, there is an increased likelihood that hazards will not be identified or adequately mitigated.
3. If aircraft that are not certified for flight in known or forecast icing conditions are dispatched into, and encounter, such conditions, there is an increased risk of degraded performance or loss of control.
4. If aircraft that are certified for flight in known or forecast icing conditions are dispatched into, and encounter, such conditions, at weights exceeding limitations, there is an increased risk of loss of control.
5. If flights are continued in known icing conditions in aircraft that are not certified to do so, there is an increased risk of degraded aircraft performance and loss of control.
6. If operators exceed aircraft manufacturers’ recommended ICEX II servicing intervals, there is an increased risk of degraded aircraft performance or loss of control resulting from greater accretion of ice on the leading-edge de-icing and propeller blade anti-icing boots.
7. If pilots do not receive the minimum required training, there is an increased risk that they will lack the necessary technical knowledge to operate aircraft safely.
8. If pilots are not provided with the information they need to calculate the aircraft’s centre of gravity accurately, they risk departing with their aircraft’s centre of gravity outside the limits, which can lead to loss of control.
9. If emergency locator transmitter antennas and cable connections are not robust enough to survive impact forces, potentially life-saving search-and-rescue operations may be impaired by the absence of a usable signal.

Other findings:
1. Wasaya’s use of a satellite aircraft flight-following system provided early warning of WSG127’s abnormal status and an accurate last known position for search-and-rescue operations.
2. The investigation could not determine whether the autopilot had been used by the pilot of WSG127 at any time during the flight.

The investigation revealed no anomalies on the part of the aircraft and all damage was attributed to the impact with the ground. The fatal injuries sustained by the pilot made it impossible to determine if the pilot was incapacitated or not. It was observed that the aircraft performed a series of unexplainable as well as erratic flying manoeuvres, which resulted in a loss of control and the aircraft to enter into a spiral dive, which was observed by the Gripen pilot before colliding with the ground.

Contributing factors:
- Control skills – undetermined
It is possible that, after inadvertent movement of the horizontal stabilizer, the crewmembers did not operate on the control switches of the secondary pitch trim system, since no other warning sound (Clacker) was recorded on the CVR recordings. The action prevised in the emergency procedures Pitch Trim Runaway or Failure, item 3, regarding trimming of the aircraft through the secondary system, possibly, was not performed. The performance of the crew may have been restricted only to the elevator control on the aircraft controls or to the control of the stabilizer associated with the primary trimming mode.
- Attitude – undetermined
The decision to make the flight without the proper functioning of the primary pitch trim and autopilot system may have been the result of the pilot's self-confidence because of the successful previous flight under similar operating conditions. Considering the hypothesis that the updated Shutdown Checklist, which should incorporate the Stabilizer Trim Backdrive Monitor - TEST, was not performed after the precrash flight, one could consider that there was a lack of adhesion to the aircraft operating procedures. Such an attitude could be associated with the pilot's self-confidence about the aircraft's operating routine, whose acquired experience could have given him the habit of ignoring some of the procedures deemed less important during the flight completion phase.
- Crew Resource Management – a contributor
Throughout the flight, there was an absence of verbalization and communication of the actions on the checklist. Similarly, in the face of the emergency situation of the horizontal stabilizer (Pitch Trim Runaway or Failure), no statements were identified regarding the actions required to manage this situation among the crew. These characteristics denote inefficiency in the use of human resources available for the aircraft operation.
- Training – undetermined
It is possible that the absence of a periodic training in simulator, especially the emergency Pitch Trim Runway or Failure, has affected the performance of the crew, as far as the CVR did not record statements related to the actions required by the abnormal condition experienced.
- Organizational culture – undetermined
The operator did not usually properly fill out the PT-WQH flight logbook. This condition evidenced the existence of informal rules regarding the monitoring of the operational conditions of the aircraft. In this context, it is possible that the history of failures related to the pitch trim system has not been registered.
- Piloting judgment – undetermined
Moments prior to takeoff, it was recorded in the CVR speeches related to the flight without the autopilot, possibly related to a failure or inoperativeness of the primary pitch trim system. The takeoff with a possible failure in the pitch trim system of the aircraft, showed an inadequate assessment of the risks involved in the operation under those conditions.
- Aircraft maintenance – undetermined
It was not possible to establish a link between the maintenance services performed on the aircraft in September 2015 and the events that resulted in the accident occurred on 10NOV2015. However, it was not ruled out that an incomplete crash survey was carried out in the pitch trim system of the aircraft, due to the lack of detail of the service orders.
- Decision-making process – a contributor
The sounds related to the test positions of the Rotary Test Switch have not been recorded in the CVR recording, so it is possible to conclude that the Warning Systems - Check item of the Cockpit Preparation Checklist has not been performed. The decision to perform the flight without the complete execution of all items of the Cockpit Preparation Checklist, prevented the correct verification of the primary longitudinal Trim system of the aircraft and reflected an inadequate judgment about the risks involved in that operation.
- Interpersonal relationship – undetermined
According to the CVR data, there was a possible rush of the crew to take-off, even though it was verified that the aircraft's pitch trim system did not work properly. It was not possible to determine if this rush was motivated by passengers’ pressure or self-imposed by the pilot.
- Support systems – undetermined
It is possible that the Pilots' Abbreviated Checklist - NORMAL PROCEDURES, aboard the aircraft, was outdated, without the incorporation of the Stabilizer Trim Backdrive Monitor - TEST procedure in the Shutdown Checklist. The possible completion of Shutdown Checklist with outdated procedures would have hampered the manufacturer's suggested verification for identification of abnormalities in the aircraft's pitch trim system.
- Managerial oversight – undetermined
The records and control of the operational check flights, both by the maintenance shop and by the operator, prevised in documentation issued by the manufacturer (SB650- 27-53 and ASL650-55-04) were not performed in an adequate manner, indicating possible weaknesses in the supervision of the maintenance activities.

The pilot's loss of airplane control due to spatial disorientation. Also causal to the accident was the pilot's impairment by the combined effects of multiple medications and drugs.

The pilot's feathering of the incorrect propeller following a total loss of right engine power due to fuel starvation, which resulted from maintenance personnel's failure to reinstall the flapper valve in the right main fuel tank. Contributing to the accident was the pilot's impairment due to alcohol consumption.

Due to lack of evidences, the exact cause of the loss of control could not be determined.